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+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+**********************************************************************
+* Copyright (C) 1999-2014, International Business Machines
+* Corporation and others. All Rights Reserved.
+**********************************************************************
+*   Date        Name        Description
+*   11/17/99    aliu        Creation.
+**********************************************************************
+*/
+#ifndef TRANSLIT_H
+#define TRANSLIT_H
+
+#include "unicode/utypes.h"
+
+#if U_SHOW_CPLUSPLUS_API
+
+/**
+ * \file
+ * \brief C++ API: Tranforms text from one format to another.
+ */
+
+#if !UCONFIG_NO_TRANSLITERATION
+
+#include "unicode/uobject.h"
+#include "unicode/unistr.h"
+#include "unicode/parseerr.h"
+#include "unicode/utrans.h" // UTransPosition, UTransDirection
+#include "unicode/strenum.h"
+
+U_NAMESPACE_BEGIN
+
+class UnicodeFilter;
+class UnicodeSet;
+class TransliteratorParser;
+class NormalizationTransliterator;
+class TransliteratorIDParser;
+
+/**
+ *
+ * <code>Transliterator</code> is an abstract class that
+ * transliterates text from one format to another.  The most common
+ * kind of transliterator is a script, or alphabet, transliterator.
+ * For example, a Russian to Latin transliterator changes Russian text
+ * written in Cyrillic characters to phonetically equivalent Latin
+ * characters.  It does not <em>translate</em> Russian to English!
+ * Transliteration, unlike translation, operates on characters, without
+ * reference to the meanings of words and sentences.
+ *
+ * <p>Although script conversion is its most common use, a
+ * transliterator can actually perform a more general class of tasks.
+ * In fact, <code>Transliterator</code> defines a very general API
+ * which specifies only that a segment of the input text is replaced
+ * by new text.  The particulars of this conversion are determined
+ * entirely by subclasses of <code>Transliterator</code>.
+ *
+ * <p><b>Transliterators are stateless</b>
+ *
+ * <p><code>Transliterator</code> objects are <em>stateless</em>; they
+ * retain no information between calls to
+ * <code>transliterate()</code>.  (However, this does <em>not</em>
+ * mean that threads may share transliterators without synchronizing
+ * them.  Transliterators are not immutable, so they must be
+ * synchronized when shared between threads.)  This might seem to
+ * limit the complexity of the transliteration operation.  In
+ * practice, subclasses perform complex transliterations by delaying
+ * the replacement of text until it is known that no other
+ * replacements are possible.  In other words, although the
+ * <code>Transliterator</code> objects are stateless, the source text
+ * itself embodies all the needed information, and delayed operation
+ * allows arbitrary complexity.
+ *
+ * <p><b>Batch transliteration</b>
+ *
+ * <p>The simplest way to perform transliteration is all at once, on a
+ * string of existing text.  This is referred to as <em>batch</em>
+ * transliteration.  For example, given a string <code>input</code>
+ * and a transliterator <code>t</code>, the call
+ *
+ *     String result = t.transliterate(input);
+ *
+ * will transliterate it and return the result.  Other methods allow
+ * the client to specify a substring to be transliterated and to use
+ * {@link Replaceable } objects instead of strings, in order to
+ * preserve out-of-band information (such as text styles).
+ *
+ * <p><b>Keyboard transliteration</b>
+ *
+ * <p>Somewhat more involved is <em>keyboard</em>, or incremental
+ * transliteration.  This is the transliteration of text that is
+ * arriving from some source (typically the user's keyboard) one
+ * character at a time, or in some other piecemeal fashion.
+ *
+ * <p>In keyboard transliteration, a <code>Replaceable</code> buffer
+ * stores the text.  As text is inserted, as much as possible is
+ * transliterated on the fly.  This means a GUI that displays the
+ * contents of the buffer may show text being modified as each new
+ * character arrives.
+ *
+ * <p>Consider the simple rule-based Transliterator:
+ * <pre>
+ *     th>{theta}
+ *     t>{tau}
+ * </pre>
+ *
+ * When the user types 't', nothing will happen, since the
+ * transliterator is waiting to see if the next character is 'h'.  To
+ * remedy this, we introduce the notion of a cursor, marked by a '|'
+ * in the output string:
+ * <pre>
+ *     t>|{tau}
+ *     {tau}h>{theta}
+ * </pre>
+ *
+ * Now when the user types 't', tau appears, and if the next character
+ * is 'h', the tau changes to a theta.  This is accomplished by
+ * maintaining a cursor position (independent of the insertion point,
+ * and invisible in the GUI) across calls to
+ * <code>transliterate()</code>.  Typically, the cursor will
+ * be coincident with the insertion point, but in a case like the one
+ * above, it will precede the insertion point.
+ *
+ * <p>Keyboard transliteration methods maintain a set of three indices
+ * that are updated with each call to
+ * <code>transliterate()</code>, including the cursor, start,
+ * and limit.  Since these indices are changed by the method, they are
+ * passed in an <code>int[]</code> array. The <code>START</code> index
+ * marks the beginning of the substring that the transliterator will
+ * look at.  It is advanced as text becomes committed (but it is not
+ * the committed index; that's the <code>CURSOR</code>).  The
+ * <code>CURSOR</code> index, described above, marks the point at
+ * which the transliterator last stopped, either because it reached
+ * the end, or because it required more characters to disambiguate
+ * between possible inputs.  The <code>CURSOR</code> can also be
+ * explicitly set by rules in a rule-based Transliterator.
+ * Any characters before the <code>CURSOR</code> index are frozen;
+ * future keyboard transliteration calls within this input sequence
+ * will not change them.  New text is inserted at the
+ * <code>LIMIT</code> index, which marks the end of the substring that
+ * the transliterator looks at.
+ *
+ * <p>Because keyboard transliteration assumes that more characters
+ * are to arrive, it is conservative in its operation.  It only
+ * transliterates when it can do so unambiguously.  Otherwise it waits
+ * for more characters to arrive.  When the client code knows that no
+ * more characters are forthcoming, perhaps because the user has
+ * performed some input termination operation, then it should call
+ * <code>finishTransliteration()</code> to complete any
+ * pending transliterations.
+ *
+ * <p><b>Inverses</b>
+ *
+ * <p>Pairs of transliterators may be inverses of one another.  For
+ * example, if transliterator <b>A</b> transliterates characters by
+ * incrementing their Unicode value (so "abc" -> "def"), and
+ * transliterator <b>B</b> decrements character values, then <b>A</b>
+ * is an inverse of <b>B</b> and vice versa.  If we compose <b>A</b>
+ * with <b>B</b> in a compound transliterator, the result is the
+ * indentity transliterator, that is, a transliterator that does not
+ * change its input text.
+ *
+ * The <code>Transliterator</code> method <code>getInverse()</code>
+ * returns a transliterator's inverse, if one exists, or
+ * <code>null</code> otherwise.  However, the result of
+ * <code>getInverse()</code> usually will <em>not</em> be a true
+ * mathematical inverse.  This is because true inverse transliterators
+ * are difficult to formulate.  For example, consider two
+ * transliterators: <b>AB</b>, which transliterates the character 'A'
+ * to 'B', and <b>BA</b>, which transliterates 'B' to 'A'.  It might
+ * seem that these are exact inverses, since
+ *
+ * \htmlonly<blockquote>\endhtmlonly"A" x <b>AB</b> -> "B"<br>
+ * "B" x <b>BA</b> -> "A"\htmlonly</blockquote>\endhtmlonly
+ *
+ * where 'x' represents transliteration.  However,
+ *
+ * \htmlonly<blockquote>\endhtmlonly"ABCD" x <b>AB</b> -> "BBCD"<br>
+ * "BBCD" x <b>BA</b> -> "AACD"\htmlonly</blockquote>\endhtmlonly
+ *
+ * so <b>AB</b> composed with <b>BA</b> is not the
+ * identity. Nonetheless, <b>BA</b> may be usefully considered to be
+ * <b>AB</b>'s inverse, and it is on this basis that
+ * <b>AB</b><code>.getInverse()</code> could legitimately return
+ * <b>BA</b>.
+ *
+ * <p><b>IDs and display names</b>
+ *
+ * <p>A transliterator is designated by a short identifier string or
+ * <em>ID</em>.  IDs follow the format <em>source-destination</em>,
+ * where <em>source</em> describes the entity being replaced, and
+ * <em>destination</em> describes the entity replacing
+ * <em>source</em>.  The entities may be the names of scripts,
+ * particular sequences of characters, or whatever else it is that the
+ * transliterator converts to or from.  For example, a transliterator
+ * from Russian to Latin might be named "Russian-Latin".  A
+ * transliterator from keyboard escape sequences to Latin-1 characters
+ * might be named "KeyboardEscape-Latin1".  By convention, system
+ * entity names are in English, with the initial letters of words
+ * capitalized; user entity names may follow any format so long as
+ * they do not contain dashes.
+ *
+ * <p>In addition to programmatic IDs, transliterator objects have
+ * display names for presentation in user interfaces, returned by
+ * {@link #getDisplayName }.
+ *
+ * <p><b>Factory methods and registration</b>
+ *
+ * <p>In general, client code should use the factory method
+ * {@link #createInstance } to obtain an instance of a
+ * transliterator given its ID.  Valid IDs may be enumerated using
+ * <code>getAvailableIDs()</code>.  Since transliterators are mutable,
+ * multiple calls to {@link #createInstance } with the same ID will
+ * return distinct objects.
+ *
+ * <p>In addition to the system transliterators registered at startup,
+ * user transliterators may be registered by calling
+ * <code>registerInstance()</code> at run time.  A registered instance
+ * acts a template; future calls to {@link #createInstance } with the ID
+ * of the registered object return clones of that object.  Thus any
+ * object passed to <tt>registerInstance()</tt> must implement
+ * <tt>clone()</tt> propertly.  To register a transliterator subclass
+ * without instantiating it (until it is needed), users may call
+ * {@link #registerFactory }.  In this case, the objects are
+ * instantiated by invoking the zero-argument public constructor of
+ * the class.
+ *
+ * <p><b>Subclassing</b>
+ *
+ * Subclasses must implement the abstract method
+ * <code>handleTransliterate()</code>.  <p>Subclasses should override
+ * the <code>transliterate()</code> method taking a
+ * <code>Replaceable</code> and the <code>transliterate()</code>
+ * method taking a <code>String</code> and <code>StringBuffer</code>
+ * if the performance of these methods can be improved over the
+ * performance obtained by the default implementations in this class.
+ *
+ * <p><b>Rule syntax</b>
+ *
+ * <p>A set of rules determines how to perform translations.
+ * Rules within a rule set are separated by semicolons (';').
+ * To include a literal semicolon, prefix it with a backslash ('\').
+ * Unicode Pattern_White_Space is ignored.
+ * If the first non-blank character on a line is '#',
+ * the entire line is ignored as a comment.
+ *
+ * <p>Each set of rules consists of two groups, one forward, and one
+ * reverse. This is a convention that is not enforced; rules for one
+ * direction may be omitted, with the result that translations in
+ * that direction will not modify the source text. In addition,
+ * bidirectional forward-reverse rules may be specified for
+ * symmetrical transformations.
+ *
+ * <p>Note: Another description of the Transliterator rule syntax is available in
+ * <a href="https://www.unicode.org/reports/tr35/tr35-general.html#Transform_Rules_Syntax">section
+ * Transform Rules Syntax of UTS #35: Unicode LDML</a>.
+ * The rules are shown there using arrow symbols ← and → and ↔.
+ * ICU supports both those and the equivalent ASCII symbols &lt; and &gt; and &lt;&gt;.
+ *
+ * <p>Rule statements take one of the following forms:
+ *
+ * <dl>
+ *     <dt><code>$alefmadda=\\u0622;</code></dt>
+ *     <dd><strong>Variable definition.</strong> The name on the
+ *         left is assigned the text on the right. In this example,
+ *         after this statement, instances of the left hand name,
+ *         &quot;<code>$alefmadda</code>&quot;, will be replaced by
+ *         the Unicode character U+0622. Variable names must begin
+ *         with a letter and consist only of letters, digits, and
+ *         underscores. Case is significant. Duplicate names cause
+ *         an exception to be thrown, that is, variables cannot be
+ *         redefined. The right hand side may contain well-formed
+ *         text of any length, including no text at all (&quot;<code>$empty=;</code>&quot;).
+ *         The right hand side may contain embedded <code>UnicodeSet</code>
+ *         patterns, for example, &quot;<code>$softvowel=[eiyEIY]</code>&quot;.</dd>
+ *     <dt><code>ai&gt;$alefmadda;</code></dt>
+ *     <dd><strong>Forward translation rule.</strong> This rule
+ *         states that the string on the left will be changed to the
+ *         string on the right when performing forward
+ *         transliteration.</dd>
+ *     <dt><code>ai&lt;$alefmadda;</code></dt>
+ *     <dd><strong>Reverse translation rule.</strong> This rule
+ *         states that the string on the right will be changed to
+ *         the string on the left when performing reverse
+ *         transliteration.</dd>
+ * </dl>
+ *
+ * <dl>
+ *     <dt><code>ai&lt;&gt;$alefmadda;</code></dt>
+ *     <dd><strong>Bidirectional translation rule.</strong> This
+ *         rule states that the string on the right will be changed
+ *         to the string on the left when performing forward
+ *         transliteration, and vice versa when performing reverse
+ *         transliteration.</dd>
+ * </dl>
+ *
+ * <p>Translation rules consist of a <em>match pattern</em> and an <em>output
+ * string</em>. The match pattern consists of literal characters,
+ * optionally preceded by context, and optionally followed by
+ * context. Context characters, like literal pattern characters,
+ * must be matched in the text being transliterated. However, unlike
+ * literal pattern characters, they are not replaced by the output
+ * text. For example, the pattern &quot;<code>abc{def}</code>&quot;
+ * indicates the characters &quot;<code>def</code>&quot; must be
+ * preceded by &quot;<code>abc</code>&quot; for a successful match.
+ * If there is a successful match, &quot;<code>def</code>&quot; will
+ * be replaced, but not &quot;<code>abc</code>&quot;. The final '<code>}</code>'
+ * is optional, so &quot;<code>abc{def</code>&quot; is equivalent to
+ * &quot;<code>abc{def}</code>&quot;. Another example is &quot;<code>{123}456</code>&quot;
+ * (or &quot;<code>123}456</code>&quot;) in which the literal
+ * pattern &quot;<code>123</code>&quot; must be followed by &quot;<code>456</code>&quot;.
+ *
+ * <p>The output string of a forward or reverse rule consists of
+ * characters to replace the literal pattern characters. If the
+ * output string contains the character '<code>|</code>', this is
+ * taken to indicate the location of the <em>cursor</em> after
+ * replacement. The cursor is the point in the text at which the
+ * next replacement, if any, will be applied. The cursor is usually
+ * placed within the replacement text; however, it can actually be
+ * placed into the precending or following context by using the
+ * special character '@'. Examples:
+ *
+ * <pre>
+ *     a {foo} z &gt; | @ bar; # foo -&gt; bar, move cursor before a
+ *     {foo} xyz &gt; bar @@|; #&nbsp;foo -&gt; bar, cursor between y and z
+ * </pre>
+ *
+ * <p><b>UnicodeSet</b>
+ *
+ * <p><code>UnicodeSet</code> patterns may appear anywhere that
+ * makes sense. They may appear in variable definitions.
+ * Contrariwise, <code>UnicodeSet</code> patterns may themselves
+ * contain variable references, such as &quot;<code>$a=[a-z];$not_a=[^$a]</code>&quot;,
+ * or &quot;<code>$range=a-z;$ll=[$range]</code>&quot;.
+ *
+ * <p><code>UnicodeSet</code> patterns may also be embedded directly
+ * into rule strings. Thus, the following two rules are equivalent:
+ *
+ * <pre>
+ *     $vowel=[aeiou]; $vowel&gt;'*'; # One way to do this
+ *     [aeiou]&gt;'*'; # Another way
+ * </pre>
+ *
+ * <p>See {@link UnicodeSet} for more documentation and examples.
+ *
+ * <p><b>Segments</b>
+ *
+ * <p>Segments of the input string can be matched and copied to the
+ * output string. This makes certain sets of rules simpler and more
+ * general, and makes reordering possible. For example:
+ *
+ * <pre>
+ *     ([a-z]) &gt; $1 $1; # double lowercase letters
+ *     ([:Lu:]) ([:Ll:]) &gt; $2 $1; # reverse order of Lu-Ll pairs
+ * </pre>
+ *
+ * <p>The segment of the input string to be copied is delimited by
+ * &quot;<code>(</code>&quot; and &quot;<code>)</code>&quot;. Up to
+ * nine segments may be defined. Segments may not overlap. In the
+ * output string, &quot;<code>$1</code>&quot; through &quot;<code>$9</code>&quot;
+ * represent the input string segments, in left-to-right order of
+ * definition.
+ *
+ * <p><b>Anchors</b>
+ *
+ * <p>Patterns can be anchored to the beginning or the end of the text. This is done with the
+ * special characters '<code>^</code>' and '<code>$</code>'. For example:
+ *
+ * <pre>
+ *   ^ a&nbsp;&nbsp; &gt; 'BEG_A'; &nbsp;&nbsp;# match 'a' at start of text
+ *   &nbsp; a&nbsp;&nbsp; &gt; 'A'; # match other instances of 'a'
+ *   &nbsp; z $ &gt; 'END_Z'; &nbsp;&nbsp;# match 'z' at end of text
+ *   &nbsp; z&nbsp;&nbsp; &gt; 'Z';&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; # match other instances of 'z'
+ * </pre>
+ *
+ * <p>It is also possible to match the beginning or the end of the text using a <code>UnicodeSet</code>.
+ * This is done by including a virtual anchor character '<code>$</code>' at the end of the
+ * set pattern. Although this is usually the match chafacter for the end anchor, the set will
+ * match either the beginning or the end of the text, depending on its placement. For
+ * example:
+ *
+ * <pre>
+ *   $x = [a-z$]; &nbsp;&nbsp;# match 'a' through 'z' OR anchor
+ *   $x 1&nbsp;&nbsp;&nbsp; &gt; 2;&nbsp;&nbsp; # match '1' after a-z or at the start
+ *   &nbsp;&nbsp; 3 $x &gt; 4; &nbsp;&nbsp;# match '3' before a-z or at the end
+ * </pre>
+ *
+ * <p><b>Example</b>
+ *
+ * <p>The following example rules illustrate many of the features of
+ * the rule language.
+ *
+ * <table border="0" cellpadding="4">
+ *     <tr>
+ *         <td style="vertical-align: top;">Rule 1.</td>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>abc{def}&gt;x|y</code></td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top;">Rule 2.</td>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>xyz&gt;r</code></td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top;">Rule 3.</td>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>yz&gt;q</code></td>
+ *     </tr>
+ * </table>
+ *
+ * <p>Applying these rules to the string &quot;<code>adefabcdefz</code>&quot;
+ * yields the following results:
+ *
+ * <table border="0" cellpadding="4">
+ *     <tr>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>|adefabcdefz</code></td>
+ *         <td style="vertical-align: top;">Initial state, no rules match. Advance
+ *         cursor.</td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>a|defabcdefz</code></td>
+ *         <td style="vertical-align: top;">Still no match. Rule 1 does not match
+ *         because the preceding context is not present.</td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>ad|efabcdefz</code></td>
+ *         <td style="vertical-align: top;">Still no match. Keep advancing until
+ *         there is a match...</td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>ade|fabcdefz</code></td>
+ *         <td style="vertical-align: top;">...</td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>adef|abcdefz</code></td>
+ *         <td style="vertical-align: top;">...</td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>adefa|bcdefz</code></td>
+ *         <td style="vertical-align: top;">...</td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>adefab|cdefz</code></td>
+ *         <td style="vertical-align: top;">...</td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>adefabc|defz</code></td>
+ *         <td style="vertical-align: top;">Rule 1 matches; replace &quot;<code>def</code>&quot;
+ *         with &quot;<code>xy</code>&quot; and back up the cursor
+ *         to before the '<code>y</code>'.</td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>adefabcx|yz</code></td>
+ *         <td style="vertical-align: top;">Although &quot;<code>xyz</code>&quot; is
+ *         present, rule 2 does not match because the cursor is
+ *         before the '<code>y</code>', not before the '<code>x</code>'.
+ *         Rule 3 does match. Replace &quot;<code>yz</code>&quot;
+ *         with &quot;<code>q</code>&quot;.</td>
+ *     </tr>
+ *     <tr>
+ *         <td style="vertical-align: top; write-space: nowrap;"><code>adefabcxq|</code></td>
+ *         <td style="vertical-align: top;">The cursor is at the end;
+ *         transliteration is complete.</td>
+ *     </tr>
+ * </table>
+ *
+ * <p>The order of rules is significant. If multiple rules may match
+ * at some point, the first matching rule is applied.
+ *
+ * <p>Forward and reverse rules may have an empty output string.
+ * Otherwise, an empty left or right hand side of any statement is a
+ * syntax error.
+ *
+ * <p>Single quotes are used to quote any character other than a
+ * digit or letter. To specify a single quote itself, inside or
+ * outside of quotes, use two single quotes in a row. For example,
+ * the rule &quot;<code>'&gt;'&gt;o''clock</code>&quot; changes the
+ * string &quot;<code>&gt;</code>&quot; to the string &quot;<code>o'clock</code>&quot;.
+ *
+ * <p><b>Notes</b>
+ *
+ * <p>While a Transliterator is being built from rules, it checks that
+ * the rules are added in proper order. For example, if the rule
+ * &quot;a&gt;x&quot; is followed by the rule &quot;ab&gt;y&quot;,
+ * then the second rule will throw an exception. The reason is that
+ * the second rule can never be triggered, since the first rule
+ * always matches anything it matches. In other words, the first
+ * rule <em>masks</em> the second rule.
+ *
+ * @author Alan Liu
+ * @stable ICU 2.0
+ */
+class U_I18N_API Transliterator : public UObject {
+
+private:
+
+    /**
+     * Programmatic name, e.g., "Latin-Arabic".
+     */
+    UnicodeString ID;
+
+    /**
+     * This transliterator's filter.  Any character for which
+     * <tt>filter.contains()</tt> returns <tt>false</tt> will not be
+     * altered by this transliterator.  If <tt>filter</tt> is
+     * <tt>null</tt> then no filtering is applied.
+     */
+    UnicodeFilter* filter;
+
+    int32_t maximumContextLength;
+
+ public:
+
+    /**
+     * A context integer or pointer for a factory function, passed by
+     * value.
+     * @stable ICU 2.4
+     */
+    union Token {
+        /**
+         * This token, interpreted as a 32-bit integer.
+         * @stable ICU 2.4
+         */
+        int32_t integer;
+        /**
+         * This token, interpreted as a native pointer.
+         * @stable ICU 2.4
+         */
+        void*   pointer;
+    };
+
+#ifndef U_HIDE_INTERNAL_API
+    /**
+     * Return a token containing an integer.
+     * @return a token containing an integer.
+     * @internal
+     */
+    inline static Token integerToken(int32_t);
+
+    /**
+     * Return a token containing a pointer.
+     * @return a token containing a pointer.
+     * @internal
+     */
+    inline static Token pointerToken(void*);
+#endif  /* U_HIDE_INTERNAL_API */
+
+    /**
+     * A function that creates and returns a Transliterator.  When
+     * invoked, it will be passed the ID string that is being
+     * instantiated, together with the context pointer that was passed
+     * in when the factory function was first registered.  Many
+     * factory functions will ignore both parameters, however,
+     * functions that are registered to more than one ID may use the
+     * ID or the context parameter to parameterize the transliterator
+     * they create.
+     * @param ID      the string identifier for this transliterator
+     * @param context a context pointer that will be stored and
+     *                later passed to the factory function when an ID matching
+     *                the registration ID is being instantiated with this factory.
+     * @stable ICU 2.4
+     */
+    typedef Transliterator* (U_EXPORT2 *Factory)(const UnicodeString& ID, Token context);
+
+protected:
+
+    /**
+     * Default constructor.
+     * @param ID the string identifier for this transliterator
+     * @param adoptedFilter the filter.  Any character for which
+     * <tt>filter.contains()</tt> returns <tt>false</tt> will not be
+     * altered by this transliterator.  If <tt>filter</tt> is
+     * <tt>null</tt> then no filtering is applied.
+     * @stable ICU 2.4
+     */
+    Transliterator(const UnicodeString& ID, UnicodeFilter* adoptedFilter);
+
+    /**
+     * Copy constructor.
+     * @stable ICU 2.4
+     */
+    Transliterator(const Transliterator&);
+
+    /**
+     * Assignment operator.
+     * @stable ICU 2.4
+     */
+    Transliterator& operator=(const Transliterator&);
+
+    /**
+     * Create a transliterator from a basic ID.  This is an ID
+     * containing only the forward direction source, target, and
+     * variant.
+     * @param id a basic ID of the form S-T or S-T/V.
+     * @param canon canonical ID to assign to the object, or
+     * NULL to leave the ID unchanged
+     * @return a newly created Transliterator or null if the ID is
+     * invalid.
+     * @stable ICU 2.4
+     */
+    static Transliterator* createBasicInstance(const UnicodeString& id,
+                                               const UnicodeString* canon);
+
+    friend class TransliteratorParser; // for parseID()
+    friend class TransliteratorIDParser; // for createBasicInstance()
+    friend class TransliteratorAlias; // for setID()
+
+public:
+
+    /**
+     * Destructor.
+     * @stable ICU 2.0
+     */
+    virtual ~Transliterator();
+
+    /**
+     * Implements Cloneable.
+     * All subclasses are encouraged to implement this method if it is
+     * possible and reasonable to do so.  Subclasses that are to be
+     * registered with the system using <tt>registerInstance()</tt>
+     * are required to implement this method.  If a subclass does not
+     * implement clone() properly and is registered with the system
+     * using registerInstance(), then the default clone() implementation
+     * will return null, and calls to createInstance() will fail.
+     *
+     * @return a copy of the object.
+     * @see #registerInstance
+     * @stable ICU 2.0
+     */
+    virtual Transliterator* clone() const;
+
+    /**
+     * Transliterates a segment of a string, with optional filtering.
+     *
+     * @param text the string to be transliterated
+     * @param start the beginning index, inclusive; <code>0 <= start
+     * <= limit</code>.
+     * @param limit the ending index, exclusive; <code>start <= limit
+     * <= text.length()</code>.
+     * @return The new limit index.  The text previously occupying <code>[start,
+     * limit)</code> has been transliterated, possibly to a string of a different
+     * length, at <code>[start, </code><em>new-limit</em><code>)</code>, where
+     * <em>new-limit</em> is the return value. If the input offsets are out of bounds,
+     * the returned value is -1 and the input string remains unchanged.
+     * @stable ICU 2.0
+     */
+    virtual int32_t transliterate(Replaceable& text,
+                                  int32_t start, int32_t limit) const;
+
+    /**
+     * Transliterates an entire string in place. Convenience method.
+     * @param text the string to be transliterated
+     * @stable ICU 2.0
+     */
+    virtual void transliterate(Replaceable& text) const;
+
+    /**
+     * Transliterates the portion of the text buffer that can be
+     * transliterated unambiguosly after new text has been inserted,
+     * typically as a result of a keyboard event.  The new text in
+     * <code>insertion</code> will be inserted into <code>text</code>
+     * at <code>index.limit</code>, advancing
+     * <code>index.limit</code> by <code>insertion.length()</code>.
+     * Then the transliterator will try to transliterate characters of
+     * <code>text</code> between <code>index.cursor</code> and
+     * <code>index.limit</code>.  Characters before
+     * <code>index.cursor</code> will not be changed.
+     *
+     * <p>Upon return, values in <code>index</code> will be updated.
+     * <code>index.start</code> will be advanced to the first
+     * character that future calls to this method will read.
+     * <code>index.cursor</code> and <code>index.limit</code> will
+     * be adjusted to delimit the range of text that future calls to
+     * this method may change.
+     *
+     * <p>Typical usage of this method begins with an initial call
+     * with <code>index.start</code> and <code>index.limit</code>
+     * set to indicate the portion of <code>text</code> to be
+     * transliterated, and <code>index.cursor == index.start</code>.
+     * Thereafter, <code>index</code> can be used without
+     * modification in future calls, provided that all changes to
+     * <code>text</code> are made via this method.
+     *
+     * <p>This method assumes that future calls may be made that will
+     * insert new text into the buffer.  As a result, it only performs
+     * unambiguous transliterations.  After the last call to this
+     * method, there may be untransliterated text that is waiting for
+     * more input to resolve an ambiguity.  In order to perform these
+     * pending transliterations, clients should call {@link
+     * #finishTransliteration } after the last call to this
+     * method has been made.
+     *
+     * @param text the buffer holding transliterated and untransliterated text
+     * @param index an array of three integers.
+     *
+     * <ul><li><code>index.start</code>: the beginning index,
+     * inclusive; <code>0 <= index.start <= index.limit</code>.
+     *
+     * <li><code>index.limit</code>: the ending index, exclusive;
+     * <code>index.start <= index.limit <= text.length()</code>.
+     * <code>insertion</code> is inserted at
+     * <code>index.limit</code>.
+     *
+     * <li><code>index.cursor</code>: the next character to be
+     * considered for transliteration; <code>index.start <=
+     * index.cursor <= index.limit</code>.  Characters before
+     * <code>index.cursor</code> will not be changed by future calls
+     * to this method.</ul>
+     *
+     * @param insertion text to be inserted and possibly
+     * transliterated into the translation buffer at
+     * <code>index.limit</code>.  If <code>null</code> then no text
+     * is inserted.
+     * @param status    Output param to filled in with a success or an error.
+     * @see #handleTransliterate
+     * @exception IllegalArgumentException if <code>index</code>
+     * is invalid
+     * @see UTransPosition
+     * @stable ICU 2.0
+     */
+    virtual void transliterate(Replaceable& text, UTransPosition& index,
+                               const UnicodeString& insertion,
+                               UErrorCode& status) const;
+
+    /**
+     * Transliterates the portion of the text buffer that can be
+     * transliterated unambiguosly after a new character has been
+     * inserted, typically as a result of a keyboard event.  This is a
+     * convenience method.
+     * @param text the buffer holding transliterated and
+     * untransliterated text
+     * @param index an array of three integers.
+     * @param insertion text to be inserted and possibly
+     * transliterated into the translation buffer at
+     * <code>index.limit</code>.
+     * @param status    Output param to filled in with a success or an error.
+     * @see #transliterate(Replaceable&, UTransPosition&, const UnicodeString&, UErrorCode&) const
+     * @stable ICU 2.0
+     */
+    virtual void transliterate(Replaceable& text, UTransPosition& index,
+                               UChar32 insertion,
+                               UErrorCode& status) const;
+
+    /**
+     * Transliterates the portion of the text buffer that can be
+     * transliterated unambiguosly.  This is a convenience method; see
+     * {@link
+     * #transliterate(Replaceable&, UTransPosition&, const UnicodeString&, UErrorCode&) const }
+     * for details.
+     * @param text the buffer holding transliterated and
+     * untransliterated text
+     * @param index an array of three integers.
+     * @param status    Output param to filled in with a success or an error.
+     * @see #transliterate(Replaceable&, UTransPosition&, const UnicodeString&, UErrorCode &) const
+     * @stable ICU 2.0
+     */
+    virtual void transliterate(Replaceable& text, UTransPosition& index,
+                               UErrorCode& status) const;
+
+    /**
+     * Finishes any pending transliterations that were waiting for
+     * more characters.  Clients should call this method as the last
+     * call after a sequence of one or more calls to
+     * <code>transliterate()</code>.
+     * @param text the buffer holding transliterated and
+     * untransliterated text.
+     * @param index the array of indices previously passed to {@link
+     * #transliterate }
+     * @stable ICU 2.0
+     */
+    virtual void finishTransliteration(Replaceable& text,
+                                       UTransPosition& index) const;
+
+private:
+
+    /**
+     * This internal method does incremental transliteration.  If the
+     * 'insertion' is non-null then we append it to 'text' before
+     * proceeding.  This method calls through to the pure virtual
+     * framework method handleTransliterate() to do the actual
+     * work.
+     * @param text the buffer holding transliterated and
+     * untransliterated text
+     * @param index an array of three integers.  See {@link
+     * #transliterate(Replaceable, int[], String)}.
+     * @param insertion text to be inserted and possibly
+     * transliterated into the translation buffer at
+     * <code>index.limit</code>.
+     * @param status    Output param to filled in with a success or an error.
+     */
+    void _transliterate(Replaceable& text,
+                        UTransPosition& index,
+                        const UnicodeString* insertion,
+                        UErrorCode &status) const;
+
+protected:
+
+    /**
+     * Abstract method that concrete subclasses define to implement
+     * their transliteration algorithm.  This method handles both
+     * incremental and non-incremental transliteration.  Let
+     * <code>originalStart</code> refer to the value of
+     * <code>pos.start</code> upon entry.
+     *
+     * <ul>
+     *  <li>If <code>incremental</code> is false, then this method
+     *  should transliterate all characters between
+     *  <code>pos.start</code> and <code>pos.limit</code>. Upon return
+     *  <code>pos.start</code> must == <code> pos.limit</code>.</li>
+     *
+     *  <li>If <code>incremental</code> is true, then this method
+     *  should transliterate all characters between
+     *  <code>pos.start</code> and <code>pos.limit</code> that can be
+     *  unambiguously transliterated, regardless of future insertions
+     *  of text at <code>pos.limit</code>.  Upon return,
+     *  <code>pos.start</code> should be in the range
+     *  [<code>originalStart</code>, <code>pos.limit</code>).
+     *  <code>pos.start</code> should be positioned such that
+     *  characters [<code>originalStart</code>, <code>
+     *  pos.start</code>) will not be changed in the future by this
+     *  transliterator and characters [<code>pos.start</code>,
+     *  <code>pos.limit</code>) are unchanged.</li>
+     * </ul>
+     *
+     * <p>Implementations of this method should also obey the
+     * following invariants:</p>
+     *
+     * <ul>
+     *  <li> <code>pos.limit</code> and <code>pos.contextLimit</code>
+     *  should be updated to reflect changes in length of the text
+     *  between <code>pos.start</code> and <code>pos.limit</code>. The
+     *  difference <code> pos.contextLimit - pos.limit</code> should
+     *  not change.</li>
+     *
+     *  <li><code>pos.contextStart</code> should not change.</li>
+     *
+     *  <li>Upon return, neither <code>pos.start</code> nor
+     *  <code>pos.limit</code> should be less than
+     *  <code>originalStart</code>.</li>
+     *
+     *  <li>Text before <code>originalStart</code> and text after
+     *  <code>pos.limit</code> should not change.</li>
+     *
+     *  <li>Text before <code>pos.contextStart</code> and text after
+     *  <code> pos.contextLimit</code> should be ignored.</li>
+     * </ul>
+     *
+     * <p>Subclasses may safely assume that all characters in
+     * [<code>pos.start</code>, <code>pos.limit</code>) are filtered.
+     * In other words, the filter has already been applied by the time
+     * this method is called.  See
+     * <code>filteredTransliterate()</code>.
+     *
+     * <p>This method is <b>not</b> for public consumption.  Calling
+     * this method directly will transliterate
+     * [<code>pos.start</code>, <code>pos.limit</code>) without
+     * applying the filter. End user code should call <code>
+     * transliterate()</code> instead of this method. Subclass code
+     * and wrapping transliterators should call
+     * <code>filteredTransliterate()</code> instead of this method.<p>
+     *
+     * @param text the buffer holding transliterated and
+     * untransliterated text
+     *
+     * @param pos the indices indicating the start, limit, context
+     * start, and context limit of the text.
+     *
+     * @param incremental if true, assume more text may be inserted at
+     * <code>pos.limit</code> and act accordingly.  Otherwise,
+     * transliterate all text between <code>pos.start</code> and
+     * <code>pos.limit</code> and move <code>pos.start</code> up to
+     * <code>pos.limit</code>.
+     *
+     * @see #transliterate
+     * @stable ICU 2.4
+     */
+    virtual void handleTransliterate(Replaceable& text,
+                                     UTransPosition& pos,
+                                     UBool incremental) const = 0;
+
+public:
+    /**
+     * Transliterate a substring of text, as specified by index, taking filters
+     * into account.  This method is for subclasses that need to delegate to
+     * another transliterator.
+     * @param text the text to be transliterated
+     * @param index the position indices
+     * @param incremental if TRUE, then assume more characters may be inserted
+     * at index.limit, and postpone processing to accomodate future incoming
+     * characters
+     * @stable ICU 2.4
+     */
+    virtual void filteredTransliterate(Replaceable& text,
+                                       UTransPosition& index,
+                                       UBool incremental) const;
+
+private:
+
+    /**
+     * Top-level transliteration method, handling filtering, incremental and
+     * non-incremental transliteration, and rollback.  All transliteration
+     * public API methods eventually call this method with a rollback argument
+     * of TRUE.  Other entities may call this method but rollback should be
+     * FALSE.
+     *
+     * <p>If this transliterator has a filter, break up the input text into runs
+     * of unfiltered characters.  Pass each run to
+     * subclass.handleTransliterate().
+     *
+     * <p>In incremental mode, if rollback is TRUE, perform a special
+     * incremental procedure in which several passes are made over the input
+     * text, adding one character at a time, and committing successful
+     * transliterations as they occur.  Unsuccessful transliterations are rolled
+     * back and retried with additional characters to give correct results.
+     *
+     * @param text the text to be transliterated
+     * @param index the position indices
+     * @param incremental if TRUE, then assume more characters may be inserted
+     * at index.limit, and postpone processing to accomodate future incoming
+     * characters
+     * @param rollback if TRUE and if incremental is TRUE, then perform special
+     * incremental processing, as described above, and undo partial
+     * transliterations where necessary.  If incremental is FALSE then this
+     * parameter is ignored.
+     */
+    virtual void filteredTransliterate(Replaceable& text,
+                                       UTransPosition& index,
+                                       UBool incremental,
+                                       UBool rollback) const;
+
+public:
+
+    /**
+     * Returns the length of the longest context required by this transliterator.
+     * This is <em>preceding</em> context.  The default implementation supplied
+     * by <code>Transliterator</code> returns zero; subclasses
+     * that use preceding context should override this method to return the
+     * correct value.  For example, if a transliterator translates "ddd" (where
+     * d is any digit) to "555" when preceded by "(ddd)", then the preceding
+     * context length is 5, the length of "(ddd)".
+     *
+     * @return The maximum number of preceding context characters this
+     * transliterator needs to examine
+     * @stable ICU 2.0
+     */
+    int32_t getMaximumContextLength(void) const;
+
+protected:
+
+    /**
+     * Method for subclasses to use to set the maximum context length.
+     * @param maxContextLength the new value to be set.
+     * @see #getMaximumContextLength
+     * @stable ICU 2.4
+     */
+    void setMaximumContextLength(int32_t maxContextLength);
+
+public:
+
+    /**
+     * Returns a programmatic identifier for this transliterator.
+     * If this identifier is passed to <code>createInstance()</code>, it
+     * will return this object, if it has been registered.
+     * @return a programmatic identifier for this transliterator.
+     * @see #registerInstance
+     * @see #registerFactory
+     * @see #getAvailableIDs
+     * @stable ICU 2.0
+     */
+    virtual const UnicodeString& getID(void) const;
+
+    /**
+     * Returns a name for this transliterator that is appropriate for
+     * display to the user in the default locale.  See {@link
+     * #getDisplayName } for details.
+     * @param ID     the string identifier for this transliterator
+     * @param result Output param to receive the display name
+     * @return       A reference to 'result'.
+     * @stable ICU 2.0
+     */
+    static UnicodeString& U_EXPORT2 getDisplayName(const UnicodeString& ID,
+                                         UnicodeString& result);
+
+    /**
+     * Returns a name for this transliterator that is appropriate for
+     * display to the user in the given locale.  This name is taken
+     * from the locale resource data in the standard manner of the
+     * <code>java.text</code> package.
+     *
+     * <p>If no localized names exist in the system resource bundles,
+     * a name is synthesized using a localized
+     * <code>MessageFormat</code> pattern from the resource data.  The
+     * arguments to this pattern are an integer followed by one or two
+     * strings.  The integer is the number of strings, either 1 or 2.
+     * The strings are formed by splitting the ID for this
+     * transliterator at the first '-'.  If there is no '-', then the
+     * entire ID forms the only string.
+     * @param ID       the string identifier for this transliterator
+     * @param inLocale the Locale in which the display name should be
+     *                 localized.
+     * @param result   Output param to receive the display name
+     * @return         A reference to 'result'.
+     * @stable ICU 2.0
+     */
+    static UnicodeString& U_EXPORT2 getDisplayName(const UnicodeString& ID,
+                                         const Locale& inLocale,
+                                         UnicodeString& result);
+
+    /**
+     * Returns the filter used by this transliterator, or <tt>NULL</tt>
+     * if this transliterator uses no filter.
+     * @return the filter used by this transliterator, or <tt>NULL</tt>
+     *         if this transliterator uses no filter.
+     * @stable ICU 2.0
+     */
+    const UnicodeFilter* getFilter(void) const;
+
+    /**
+     * Returns the filter used by this transliterator, or <tt>NULL</tt> if this
+     * transliterator uses no filter.  The caller must eventually delete the
+     * result.  After this call, this transliterator's filter is set to
+     * <tt>NULL</tt>.
+     * @return the filter used by this transliterator, or <tt>NULL</tt> if this
+     *         transliterator uses no filter.
+     * @stable ICU 2.4
+     */
+    UnicodeFilter* orphanFilter(void);
+
+    /**
+     * Changes the filter used by this transliterator.  If the filter
+     * is set to <tt>null</tt> then no filtering will occur.
+     *
+     * <p>Callers must take care if a transliterator is in use by
+     * multiple threads.  The filter should not be changed by one
+     * thread while another thread may be transliterating.
+     * @param adoptedFilter the new filter to be adopted.
+     * @stable ICU 2.0
+     */
+    void adoptFilter(UnicodeFilter* adoptedFilter);
+
+    /**
+     * Returns this transliterator's inverse.  See the class
+     * documentation for details.  This implementation simply inverts
+     * the two entities in the ID and attempts to retrieve the
+     * resulting transliterator.  That is, if <code>getID()</code>
+     * returns "A-B", then this method will return the result of
+     * <code>createInstance("B-A")</code>, or <code>null</code> if that
+     * call fails.
+     *
+     * <p>Subclasses with knowledge of their inverse may wish to
+     * override this method.
+     *
+     * @param status Output param to filled in with a success or an error.
+     * @return a transliterator that is an inverse, not necessarily
+     * exact, of this transliterator, or <code>null</code> if no such
+     * transliterator is registered.
+     * @see #registerInstance
+     * @stable ICU 2.0
+     */
+    Transliterator* createInverse(UErrorCode& status) const;
+
+    /**
+     * Returns a <code>Transliterator</code> object given its ID.
+     * The ID must be either a system transliterator ID or a ID registered
+     * using <code>registerInstance()</code>.
+     *
+     * @param ID a valid ID, as enumerated by <code>getAvailableIDs()</code>
+     * @param dir        either FORWARD or REVERSE.
+     * @param parseError Struct to recieve information on position
+     *                   of error if an error is encountered
+     * @param status     Output param to filled in with a success or an error.
+     * @return A <code>Transliterator</code> object with the given ID
+     * @see #registerInstance
+     * @see #getAvailableIDs
+     * @see #getID
+     * @stable ICU 2.0
+     */
+    static Transliterator* U_EXPORT2 createInstance(const UnicodeString& ID,
+                                          UTransDirection dir,
+                                          UParseError& parseError,
+                                          UErrorCode& status);
+
+    /**
+     * Returns a <code>Transliterator</code> object given its ID.
+     * The ID must be either a system transliterator ID or a ID registered
+     * using <code>registerInstance()</code>.
+     * @param ID a valid ID, as enumerated by <code>getAvailableIDs()</code>
+     * @param dir        either FORWARD or REVERSE.
+     * @param status     Output param to filled in with a success or an error.
+     * @return A <code>Transliterator</code> object with the given ID
+     * @stable ICU 2.0
+     */
+    static Transliterator* U_EXPORT2 createInstance(const UnicodeString& ID,
+                                          UTransDirection dir,
+                                          UErrorCode& status);
+
+    /**
+     * Returns a <code>Transliterator</code> object constructed from
+     * the given rule string.  This will be a rule-based Transliterator,
+     * if the rule string contains only rules, or a
+     * compound Transliterator, if it contains ID blocks, or a
+     * null Transliterator, if it contains ID blocks which parse as
+     * empty for the given direction.
+     *
+     * @param ID            the id for the transliterator.
+     * @param rules         rules, separated by ';'
+     * @param dir           either FORWARD or REVERSE.
+     * @param parseError    Struct to receive information on position
+     *                      of error if an error is encountered
+     * @param status        Output param set to success/failure code.
+     * @return a newly created Transliterator
+     * @stable ICU 2.0
+     */
+    static Transliterator* U_EXPORT2 createFromRules(const UnicodeString& ID,
+                                           const UnicodeString& rules,
+                                           UTransDirection dir,
+                                           UParseError& parseError,
+                                           UErrorCode& status);
+
+    /**
+     * Create a rule string that can be passed to createFromRules()
+     * to recreate this transliterator.
+     * @param result the string to receive the rules.  Previous
+     * contents will be deleted.
+     * @param escapeUnprintable if TRUE then convert unprintable
+     * character to their hex escape representations, \\uxxxx or
+     * \\Uxxxxxxxx.  Unprintable characters are those other than
+     * U+000A, U+0020..U+007E.
+     * @stable ICU 2.0
+     */
+    virtual UnicodeString& toRules(UnicodeString& result,
+                                   UBool escapeUnprintable) const;
+
+    /**
+     * Return the number of elements that make up this transliterator.
+     * For example, if the transliterator "NFD;Jamo-Latin;Latin-Greek"
+     * were created, the return value of this method would be 3.
+     *
+     * <p>If this transliterator is not composed of other
+     * transliterators, then this method returns 1.
+     * @return the number of transliterators that compose this
+     * transliterator, or 1 if this transliterator is not composed of
+     * multiple transliterators
+     * @stable ICU 3.0
+     */
+    int32_t countElements() const;
+
+    /**
+     * Return an element that makes up this transliterator.  For
+     * example, if the transliterator "NFD;Jamo-Latin;Latin-Greek"
+     * were created, the return value of this method would be one
+     * of the three transliterator objects that make up that
+     * transliterator: [NFD, Jamo-Latin, Latin-Greek].
+     *
+     * <p>If this transliterator is not composed of other
+     * transliterators, then this method will return a reference to
+     * this transliterator when given the index 0.
+     * @param index a value from 0..countElements()-1 indicating the
+     * transliterator to return
+     * @param ec input-output error code
+     * @return one of the transliterators that makes up this
+     * transliterator, if this transliterator is made up of multiple
+     * transliterators, otherwise a reference to this object if given
+     * an index of 0
+     * @stable ICU 3.0
+     */
+    const Transliterator& getElement(int32_t index, UErrorCode& ec) const;
+
+    /**
+     * Returns the set of all characters that may be modified in the
+     * input text by this Transliterator.  This incorporates this
+     * object's current filter; if the filter is changed, the return
+     * value of this function will change.  The default implementation
+     * returns an empty set.  Some subclasses may override {@link
+     * #handleGetSourceSet } to return a more precise result.  The
+     * return result is approximate in any case and is intended for
+     * use by tests, tools, or utilities.
+     * @param result receives result set; previous contents lost
+     * @return a reference to result
+     * @see #getTargetSet
+     * @see #handleGetSourceSet
+     * @stable ICU 2.4
+     */
+    UnicodeSet& getSourceSet(UnicodeSet& result) const;
+
+    /**
+     * Framework method that returns the set of all characters that
+     * may be modified in the input text by this Transliterator,
+     * ignoring the effect of this object's filter.  The base class
+     * implementation returns the empty set.  Subclasses that wish to
+     * implement this should override this method.
+     * @return the set of characters that this transliterator may
+     * modify.  The set may be modified, so subclasses should return a
+     * newly-created object.
+     * @param result receives result set; previous contents lost
+     * @see #getSourceSet
+     * @see #getTargetSet
+     * @stable ICU 2.4
+     */
+    virtual void handleGetSourceSet(UnicodeSet& result) const;
+
+    /**
+     * Returns the set of all characters that may be generated as
+     * replacement text by this transliterator.  The default
+     * implementation returns the empty set.  Some subclasses may
+     * override this method to return a more precise result.  The
+     * return result is approximate in any case and is intended for
+     * use by tests, tools, or utilities requiring such
+     * meta-information.
+     * @param result receives result set; previous contents lost
+     * @return a reference to result
+     * @see #getTargetSet
+     * @stable ICU 2.4
+     */
+    virtual UnicodeSet& getTargetSet(UnicodeSet& result) const;
+
+public:
+
+    /**
+     * Registers a factory function that creates transliterators of
+     * a given ID.
+     *
+     * Because ICU may choose to cache Transliterators internally, this must
+     * be called at application startup, prior to any calls to
+     * Transliterator::createXXX to avoid undefined behavior.
+     *
+     * @param id the ID being registered
+     * @param factory a function pointer that will be copied and
+     * called later when the given ID is passed to createInstance()
+     * @param context a context pointer that will be stored and
+     * later passed to the factory function when an ID matching
+     * the registration ID is being instantiated with this factory.
+     * @stable ICU 2.0
+     */
+    static void U_EXPORT2 registerFactory(const UnicodeString& id,
+                                Factory factory,
+                                Token context);
+
+    /**
+     * Registers an instance <tt>obj</tt> of a subclass of
+     * <code>Transliterator</code> with the system.  When
+     * <tt>createInstance()</tt> is called with an ID string that is
+     * equal to <tt>obj->getID()</tt>, then <tt>obj->clone()</tt> is
+     * returned.
+     *
+     * After this call the Transliterator class owns the adoptedObj
+     * and will delete it.
+     *
+     * Because ICU may choose to cache Transliterators internally, this must
+     * be called at application startup, prior to any calls to
+     * Transliterator::createXXX to avoid undefined behavior.
+     *
+     * @param adoptedObj an instance of subclass of
+     * <code>Transliterator</code> that defines <tt>clone()</tt>
+     * @see #createInstance
+     * @see #registerFactory
+     * @see #unregister
+     * @stable ICU 2.0
+     */
+    static void U_EXPORT2 registerInstance(Transliterator* adoptedObj);
+
+    /**
+     * Registers an ID string as an alias of another ID string.
+     * That is, after calling this function, <tt>createInstance(aliasID)</tt>
+     * will return the same thing as <tt>createInstance(realID)</tt>.
+     * This is generally used to create shorter, more mnemonic aliases
+     * for long compound IDs.
+     *
+     * @param aliasID The new ID being registered.
+     * @param realID The ID that the new ID is to be an alias for.
+     * This can be a compound ID and can include filters and should
+     * refer to transliterators that have already been registered with
+     * the framework, although this isn't checked.
+     * @stable ICU 3.6
+     */
+     static void U_EXPORT2 registerAlias(const UnicodeString& aliasID,
+                                         const UnicodeString& realID);
+
+protected:
+
+#ifndef U_HIDE_INTERNAL_API
+    /**
+     * @param id the ID being registered
+     * @param factory a function pointer that will be copied and
+     * called later when the given ID is passed to createInstance()
+     * @param context a context pointer that will be stored and
+     * later passed to the factory function when an ID matching
+     * the registration ID is being instantiated with this factory.
+     * @internal
+     */
+    static void _registerFactory(const UnicodeString& id,
+                                 Factory factory,
+                                 Token context);
+
+    /**
+     * @internal
+     */
+    static void _registerInstance(Transliterator* adoptedObj);
+
+    /**
+     * @internal
+     */
+    static void _registerAlias(const UnicodeString& aliasID, const UnicodeString& realID);
+
+    /**
+     * Register two targets as being inverses of one another.  For
+     * example, calling registerSpecialInverse("NFC", "NFD", true) causes
+     * Transliterator to form the following inverse relationships:
+     *
+     * <pre>NFC => NFD
+     * Any-NFC => Any-NFD
+     * NFD => NFC
+     * Any-NFD => Any-NFC</pre>
+     *
+     * (Without the special inverse registration, the inverse of NFC
+     * would be NFC-Any.)  Note that NFD is shorthand for Any-NFD, but
+     * that the presence or absence of "Any-" is preserved.
+     *
+     * <p>The relationship is symmetrical; registering (a, b) is
+     * equivalent to registering (b, a).
+     *
+     * <p>The relevant IDs must still be registered separately as
+     * factories or classes.
+     *
+     * <p>Only the targets are specified.  Special inverses always
+     * have the form Any-Target1 <=> Any-Target2.  The target should
+     * have canonical casing (the casing desired to be produced when
+     * an inverse is formed) and should contain no whitespace or other
+     * extraneous characters.
+     *
+     * @param target the target against which to register the inverse
+     * @param inverseTarget the inverse of target, that is
+     * Any-target.getInverse() => Any-inverseTarget
+     * @param bidirectional if true, register the reverse relation
+     * as well, that is, Any-inverseTarget.getInverse() => Any-target
+     * @internal
+     */
+    static void _registerSpecialInverse(const UnicodeString& target,
+                                        const UnicodeString& inverseTarget,
+                                        UBool bidirectional);
+#endif  /* U_HIDE_INTERNAL_API */
+
+public:
+
+    /**
+     * Unregisters a transliterator or class.  This may be either
+     * a system transliterator or a user transliterator or class.
+     * Any attempt to construct an unregistered transliterator based
+     * on its ID will fail.
+     *
+     * Because ICU may choose to cache Transliterators internally, this should
+     * be called during application shutdown, after all calls to
+     * Transliterator::createXXX to avoid undefined behavior.
+     *
+     * @param ID the ID of the transliterator or class
+     * @return the <code>Object</code> that was registered with
+     * <code>ID</code>, or <code>null</code> if none was
+     * @see #registerInstance
+     * @see #registerFactory
+     * @stable ICU 2.0
+     */
+    static void U_EXPORT2 unregister(const UnicodeString& ID);
+
+public:
+
+    /**
+     * Return a StringEnumeration over the IDs available at the time of the
+     * call, including user-registered IDs.
+     * @param ec input-output error code
+     * @return a newly-created StringEnumeration over the transliterators
+     * available at the time of the call. The caller should delete this object
+     * when done using it.
+     * @stable ICU 3.0
+     */
+    static StringEnumeration* U_EXPORT2 getAvailableIDs(UErrorCode& ec);
+
+    /**
+     * Return the number of registered source specifiers.
+     * @return the number of registered source specifiers.
+     * @stable ICU 2.0
+     */
+    static int32_t U_EXPORT2 countAvailableSources(void);
+
+    /**
+     * Return a registered source specifier.
+     * @param index which specifier to return, from 0 to n-1, where
+     * n = countAvailableSources()
+     * @param result fill-in paramter to receive the source specifier.
+     * If index is out of range, result will be empty.
+     * @return reference to result
+     * @stable ICU 2.0
+     */
+    static UnicodeString& U_EXPORT2 getAvailableSource(int32_t index,
+                                             UnicodeString& result);
+
+    /**
+     * Return the number of registered target specifiers for a given
+     * source specifier.
+     * @param source the given source specifier.
+     * @return the number of registered target specifiers for a given
+     *         source specifier.
+     * @stable ICU 2.0
+     */
+    static int32_t U_EXPORT2 countAvailableTargets(const UnicodeString& source);
+
+    /**
+     * Return a registered target specifier for a given source.
+     * @param index which specifier to return, from 0 to n-1, where
+     * n = countAvailableTargets(source)
+     * @param source the source specifier
+     * @param result fill-in paramter to receive the target specifier.
+     * If source is invalid or if index is out of range, result will
+     * be empty.
+     * @return reference to result
+     * @stable ICU 2.0
+     */
+    static UnicodeString& U_EXPORT2 getAvailableTarget(int32_t index,
+                                             const UnicodeString& source,
+                                             UnicodeString& result);
+
+    /**
+     * Return the number of registered variant specifiers for a given
+     * source-target pair.
+     * @param source    the source specifiers.
+     * @param target    the target specifiers.
+     * @stable ICU 2.0
+     */
+    static int32_t U_EXPORT2 countAvailableVariants(const UnicodeString& source,
+                                          const UnicodeString& target);
+
+    /**
+     * Return a registered variant specifier for a given source-target
+     * pair.
+     * @param index which specifier to return, from 0 to n-1, where
+     * n = countAvailableVariants(source, target)
+     * @param source the source specifier
+     * @param target the target specifier
+     * @param result fill-in paramter to receive the variant
+     * specifier.  If source is invalid or if target is invalid or if
+     * index is out of range, result will be empty.
+     * @return reference to result
+     * @stable ICU 2.0
+     */
+    static UnicodeString& U_EXPORT2 getAvailableVariant(int32_t index,
+                                              const UnicodeString& source,
+                                              const UnicodeString& target,
+                                              UnicodeString& result);
+
+protected:
+
+#ifndef U_HIDE_INTERNAL_API
+    /**
+     * Non-mutexed internal method
+     * @internal
+     */
+    static int32_t _countAvailableSources(void);
+
+    /**
+     * Non-mutexed internal method
+     * @internal
+     */
+    static UnicodeString& _getAvailableSource(int32_t index,
+                                              UnicodeString& result);
+
+    /**
+     * Non-mutexed internal method
+     * @internal
+     */
+    static int32_t _countAvailableTargets(const UnicodeString& source);
+
+    /**
+     * Non-mutexed internal method
+     * @internal
+     */
+    static UnicodeString& _getAvailableTarget(int32_t index,
+                                              const UnicodeString& source,
+                                              UnicodeString& result);
+
+    /**
+     * Non-mutexed internal method
+     * @internal
+     */
+    static int32_t _countAvailableVariants(const UnicodeString& source,
+                                           const UnicodeString& target);
+
+    /**
+     * Non-mutexed internal method
+     * @internal
+     */
+    static UnicodeString& _getAvailableVariant(int32_t index,
+                                               const UnicodeString& source,
+                                               const UnicodeString& target,
+                                               UnicodeString& result);
+#endif  /* U_HIDE_INTERNAL_API */
+
+protected:
+
+    /**
+     * Set the ID of this transliterators.  Subclasses shouldn't do
+     * this, unless the underlying script behavior has changed.
+     * @param id the new id t to be set.
+     * @stable ICU 2.4
+     */
+    void setID(const UnicodeString& id);
+
+public:
+
+    /**
+     * Return the class ID for this class.  This is useful only for
+     * comparing to a return value from getDynamicClassID().
+     * Note that Transliterator is an abstract base class, and therefor
+     * no fully constructed object will  have a dynamic
+     * UCLassID that equals the UClassID returned from
+     * TRansliterator::getStaticClassID().
+     * @return       The class ID for class Transliterator.
+     * @stable ICU 2.0
+     */
+    static UClassID U_EXPORT2 getStaticClassID(void);
+
+    /**
+     * Returns a unique class ID <b>polymorphically</b>.  This method
+     * is to implement a simple version of RTTI, since not all C++
+     * compilers support genuine RTTI.  Polymorphic operator==() and
+     * clone() methods call this method.
+     *
+     * <p>Concrete subclasses of Transliterator must use the
+     *    UOBJECT_DEFINE_RTTI_IMPLEMENTATION macro from
+     *    uobject.h to provide the RTTI functions.
+     *
+     * @return The class ID for this object. All objects of a given
+     * class have the same class ID.  Objects of other classes have
+     * different class IDs.
+     * @stable ICU 2.0
+     */
+    virtual UClassID getDynamicClassID(void) const = 0;
+
+private:
+    static UBool initializeRegistry(UErrorCode &status);
+
+public:
+#ifndef U_HIDE_OBSOLETE_API
+    /**
+     * Return the number of IDs currently registered with the system.
+     * To retrieve the actual IDs, call getAvailableID(i) with
+     * i from 0 to countAvailableIDs() - 1.
+     * @return the number of IDs currently registered with the system.
+     * @obsolete ICU 3.4 use getAvailableIDs() instead
+     */
+    static int32_t U_EXPORT2 countAvailableIDs(void);
+
+    /**
+     * Return the index-th available ID.  index must be between 0
+     * and countAvailableIDs() - 1, inclusive.  If index is out of
+     * range, the result of getAvailableID(0) is returned.
+     * @param index the given ID index.
+     * @return      the index-th available ID.  index must be between 0
+     *              and countAvailableIDs() - 1, inclusive.  If index is out of
+     *              range, the result of getAvailableID(0) is returned.
+     * @obsolete ICU 3.4 use getAvailableIDs() instead; this function
+     * is not thread safe, since it returns a reference to storage that
+     * may become invalid if another thread calls unregister
+     */
+    static const UnicodeString& U_EXPORT2 getAvailableID(int32_t index);
+#endif  /* U_HIDE_OBSOLETE_API */
+};
+
+inline int32_t Transliterator::getMaximumContextLength(void) const {
+    return maximumContextLength;
+}
+
+inline void Transliterator::setID(const UnicodeString& id) {
+    ID = id;
+    // NUL-terminate the ID string, which is a non-aliased copy.
+    ID.append((char16_t)0);
+    ID.truncate(ID.length()-1);
+}
+
+#ifndef U_HIDE_INTERNAL_API
+inline Transliterator::Token Transliterator::integerToken(int32_t i) {
+    Token t;
+    t.integer = i;
+    return t;
+}
+
+inline Transliterator::Token Transliterator::pointerToken(void* p) {
+    Token t;
+    t.pointer = p;
+    return t;
+}
+#endif  /* U_HIDE_INTERNAL_API */
+
+U_NAMESPACE_END
+
+#endif /* #if !UCONFIG_NO_TRANSLITERATION */
+
+#endif /* U_SHOW_CPLUSPLUS_API */
+
+#endif