/* * Copyright (C) 2014 The Android Open Source Project * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util.regex; import libcore.util.NativeAllocationRegistry; import java.util.Iterator; import java.util.ArrayList; import java.util.NoSuchElementException; import java.util.Spliterator; import java.util.Spliterators; import java.util.function.Predicate; import java.util.stream.Stream; import java.util.stream.StreamSupport; import libcore.util.EmptyArray; /** * A compiled representation of a regular expression. * *

A regular expression, specified as a string, must first be compiled into * an instance of this class. The resulting pattern can then be used to create * a {@link Matcher} object that can match arbitrary {@link * java.lang.CharSequence character sequences} against the regular * expression. All of the state involved in performing a match resides in the * matcher, so many matchers can share the same pattern. * *

A typical invocation sequence is thus * *

 * Pattern p = Pattern.{@link #compile compile}("a*b");
 * Matcher m = p.{@link #matcher matcher}("aaaaab");
 * boolean b = m.{@link Matcher#matches matches}();


 *
 *  A {@link #matches matches} method is defined by this class as a
 * convenience for when a regular expression is used just once.  This method
 * compiles an expression and matches an input sequence against it in a single
 * invocation.  The statement
 *
 * 
 * boolean b = Pattern.matches("a*b", "aaaaab");
 *
 * is equivalent to the three statements above, though for repeated matches it
 * is less efficient since it does not allow the compiled pattern to be reused.
 *
 *  Instances of this class are immutable and are safe for use by multiple
 * concurrent threads.  Instances of the {@link Matcher} class are not safe for
 * such use.
 *
 *
 * 
 * 
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 * Construct Matches
 
Characters
x The character x
\\ The backslash character
\0n The character with octal value 0n
 *         (0 <= n <= 7)
\0nn The character with octal value 0nn
 *         (0 <= n <= 7)
\0mnn The character with octal value 0mnn
 *         (0 <= m <= 3,
 *         0 <= n <= 7)
\xhh The character with hexadecimal value 0xhh
\uhhhh The character with hexadecimal value 0xhhhh
\x{h...h} The character with hexadecimal value 0xh...h
 *         ({@link java.lang.Character#MIN_CODE_POINT Character.MIN_CODE_POINT}
 *          <= 0xh...h <= 
 *          {@link java.lang.Character#MAX_CODE_POINT Character.MAX_CODE_POINT})
\t The tab character ('\u0009')
\n The newline (line feed) character ('\u000A')
\r The carriage-return character ('\u000D')
\f The form-feed character ('\u000C')
\a The alert (bell) character ('\u0007')
\e The escape character ('\u001B')
\cx The control character corresponding to x
 
Character classes
[abc] a, b, or c (simple class)
[^abc] Any character except a, b, or c (negation)
[a-zA-Z] a through z
 *         or A through Z, inclusive (range)
[a-d[m-p]] a through d,
 *      or m through p: [a-dm-p] (union)
[a-z&&[def]] d, e, or f (intersection)
[a-z&&[^bc]] a through z,
 *         except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]] a through z,
 *          and not m through p: [a-lq-z](subtraction)
 
Predefined character classes
. Any character (may or may not match line terminators)
\d A digit: [0-9]
\D A non-digit: [^0-9]
\s A whitespace character: [ \t\n\x0B\f\r]
\S A non-whitespace character: [^\s]
\w A word character: [a-zA-Z_0-9]
\W A non-word character: [^\w]
 
POSIX character classes (US-ASCII only)
\p{Lower} A lower-case alphabetic character: [a-z]
\p{Upper} An upper-case alphabetic character:[A-Z]
\p{ASCII} All ASCII:[\x00-\x7F]
\p{Alpha} An alphabetic character:[\p{Lower}\p{Upper}]
\p{Digit} A decimal digit: [0-9]
\p{Alnum} An alphanumeric character:[\p{Alpha}\p{Digit}]
\p{Punct} Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
\p{Graph} A visible character: [\p{Alnum}\p{Punct}]
\p{Print} A printable character: [\p{Graph}\x20]
\p{Blank} A space or a tab: [ \t]
\p{Cntrl} A control character: [\x00-\x1F\x7F]
\p{XDigit} A hexadecimal digit: [0-9a-fA-F]
\p{Space} A whitespace character: [ \t\n\x0B\f\r]
 
java.lang.Character classes (simple java character type)
\p{javaLowerCase} Equivalent to java.lang.Character.isLowerCase()
\p{javaUpperCase} Equivalent to java.lang.Character.isUpperCase()
\p{javaWhitespace} Equivalent to java.lang.Character.isWhitespace()
\p{javaMirrored} Equivalent to java.lang.Character.isMirrored()
 
Classes for Unicode scripts, blocks, categories and binary properties
\p{IsLatin} A Latin script character (script)
\p{InGreek} A character in the Greek block (block)
\p{Lu} An uppercase letter (category)
\p{IsAlphabetic} An alphabetic character (binary property)
\p{Sc} A currency symbol
\P{InGreek} Any character except one in the Greek block (negation)
[\p{L}&&[^\p{Lu}]]  Any letter except an uppercase letter (subtraction)
 
Boundary matchers
^ The beginning of a line
$ The end of a line
\b A word boundary
\B A non-word boundary
\A The beginning of the input
\G The end of the previous match
\Z The end of the input but for the final
 *         terminator, if any
\z The end of the input
 
Greedy quantifiers
X? X, once or not at all
X* X, zero or more times
X+ X, one or more times
X{n} X, exactly n times
X{n,} X, at least n times
X{n,m} X, at least n but not more than m times
 
Reluctant quantifiers
X?? X, once or not at all
X*? X, zero or more times
X+? X, one or more times
X{n}? X, exactly n times
X{n,}? X, at least n times
X{n,m}? X, at least n but not more than m times
 
Possessive quantifiers
X?+ X, once or not at all
X*+ X, zero or more times
X++ X, one or more times
X{n}+ X, exactly n times
X{n,}+ X, at least n times
X{n,m}+ X, at least n but not more than m times
 
Logical operators
XY X followed by Y
X|Y Either X or Y
(X) X, as a capturing group
 
Back references
\n Whatever the n^th
 *     capturing group matched
\k<name> Whatever the
 *     named-capturing group "name" matched
 
Quotation
\ Nothing, but quotes the following character
\Q Nothing, but quotes all characters until \E
\E Nothing, but ends quoting started by \Q
 
Special constructs (named-capturing and non-capturing)
(?<name>X) X, as a named-capturing group
(?:X) X, as a non-capturing group
(?idmsuxU-idmsuxU)  Nothing, but turns match flags i
 * d m s
 * u x U
 * on - off
(?idmsux-idmsux:X)   X, as a non-capturing group with the
 *         given flags i d
 * m s u
 * x on - off
(?=X) X, via zero-width positive lookahead
(?!X) X, via zero-width negative lookahead
(?<=X) X, via zero-width positive lookbehind
(?<!X) X, via zero-width negative lookbehind
(?>X) X, as an independent, non-capturing group
 *
 * 
 *
 *
 * 
 *  Backslashes, escapes, and quoting 
 *
 *  The backslash character ('\') serves to introduce escaped
 * constructs, as defined in the table above, as well as to quote characters
 * that otherwise would be interpreted as unescaped constructs.  Thus the
 * expression \\ matches a single backslash and \{ matches a
 * left brace.
 *
 * 
 It is an error to use a backslash prior to any alphabetic character that
 * does not denote an escaped construct; these are reserved for future
 * extensions to the regular-expression language.  A backslash may be used
 * prior to a non-alphabetic character regardless of whether that character is
 * part of an unescaped construct.
 *
 *  Backslashes within string literals in Java source code are interpreted
 * as required by
 * The Java™ Language Specification
 * as either Unicode escapes (section 3.3) or other character escapes (section 3.10.6)
 * It is therefore necessary to double backslashes in string
 * literals that represent regular expressions to protect them from
 * interpretation by the Java bytecode compiler.  The string literal
 * "\b", for example, matches a single backspace character when
 * interpreted as a regular expression, while "\\b" matches a
 * word boundary.  The string literal "\(hello\)" is illegal
 * and leads to a compile-time error; in order to match the string
 * (hello) the string literal "\\(hello\\)"
 * must be used.
 *
 * 
 * 
 Character Classes 

 *
 *     Character classes may appear within other character classes, and
 *    may be composed by the union operator (implicit) and the intersection
 *    operator (&&).
 *    The union operator denotes a class that contains every character that is
 *    in at least one of its operand classes.  The intersection operator
 *    denotes a class that contains every character that is in both of its
 *    operand classes.
 *
 *    
 The precedence of character-class operators is as follows, from
 *    highest to lowest:
 *
 *    

 *      
 *        
 *        
 *     
 *        
 *        
 *     
 *        
 *        
 *      
 *        
 *        
 *      
 *        
 *        
 *    1     Literal escape     \x
2     Grouping [...]
3     Range a-z
4     Union [a-e][i-u]
5     Intersection [a-z&&[aeiou]]
 *
 *     Note that a different set of metacharacters are in effect inside
 *    a character class than outside a character class. For instance, the
 *    regular expression . loses its special meaning inside a
 *    character class, while the expression - becomes a range
 *    forming metacharacter.
 *
 * 
 * 
 Line terminators 

 *
 *  A line terminator is a one- or two-character sequence that marks
 * the end of a line of the input character sequence.  The following are
 * recognized as line terminators:
 *
 * 

 *
 *    A newline (line feed) character ('\n'),
 *
 *   
 A carriage-return character followed immediately by a newline
 *   character ("\r\n"),
 *
 *   
 A standalone carriage-return character ('\r'),
 *
 *   
 A next-line character ('\u0085'),
 *
 *   
 A line-separator character ('\u2028'), or
 *
 *   
 A paragraph-separator character ('\u2029).
 *
 * 
 * If {@link #UNIX_LINES} mode is activated, then the only line terminators
 * recognized are newline characters.
 *
 * 
 The regular expression . matches any character except a line
 * terminator unless the {@link #DOTALL} flag is specified.
 *
 *  By default, the regular expressions ^ and $ ignore
 * line terminators and only match at the beginning and the end, respectively,
 * of the entire input sequence. If {@link #MULTILINE} mode is activated then
 * ^ matches at the beginning of input and after any line terminator
 * except at the end of input. When in {@link #MULTILINE} mode $
 * matches just before a line terminator or the end of the input sequence.
 *
 * 
 * 
 Groups and capturing 

 *
 * 
 *  Group number 
 *  Capturing groups are numbered by counting their opening parentheses from
 * left to right.  In the expression ((A)(B(C))), for example, there
 * are four such groups: 
 *
 * 
 * 
 *     
 * 
 *     
 * 
 *     
 * 
 *     
 * 1     ((A)(B(C)))
2     (A)
3     (B(C))
4     (C)
 *
 *  Group zero always stands for the entire expression.
 *
 *  Capturing groups are so named because, during a match, each subsequence
 * of the input sequence that matches such a group is saved.  The captured
 * subsequence may be used later in the expression, via a back reference, and
 * may also be retrieved from the matcher once the match operation is complete.
 *
 * 
 * 
 Group name 

 * A capturing group can also be assigned a "name", a named-capturing group,
 * and then be back-referenced later by the "name". Group names are composed of
 * the following characters. The first character must be a letter.
 *
 * 

 *    The uppercase letters 'A' through 'Z'
 *        ('\u0041' through '\u005a'),
 *   
 The lowercase letters 'a' through 'z'
 *        ('\u0061' through '\u007a'),
 *   
 The digits '0' through '9'
 *        ('\u0030' through '\u0039'),
 * 
 *
 *  A named-capturing group is still numbered as described in
 * Group number.
 *
 * 
 The captured input associated with a group is always the subsequence
 * that the group most recently matched.  If a group is evaluated a second time
 * because of quantification then its previously-captured value, if any, will
 * be retained if the second evaluation fails.  Matching the string
 * "aba" against the expression (a(b)?)+, for example, leaves
 * group two set to "b".  All captured input is discarded at the
 * beginning of each match.
 *
 * 
 Groups beginning with (? are either pure, non-capturing groups
 * that do not capture text and do not count towards the group total, or
 * named-capturing group.
 *
 * 
 Unicode support 
 *
 *  This class is in conformance with Level 1 of Unicode Technical
 * Standard #18: Unicode Regular Expression, plus RL2.1
 * Canonical Equivalents.
 * 

 * Unicode escape sequences such as \u2014 in Java source code
 * are processed as described in section 3.3 of
 * The Java™ Language Specification.
 * Such escape sequences are also implemented directly by the regular-expression
 * parser so that Unicode escapes can be used in expressions that are read from
 * files or from the keyboard.  Thus the strings "\u2014" and
 * "\\u2014", while not equal, compile into the same pattern, which
 * matches the character with hexadecimal value 0x2014.
 * 

 * A Unicode character can also be represented in a regular-expression by
 * using its Hex notation(hexadecimal code point value) directly as described in construct
 * \x{...}, for example a supplementary character U+2011F
 * can be specified as \x{2011F}, instead of two consecutive
 * Unicode escape sequences of the surrogate pair
 * \uD840\uDD1F.
 * 

 * Unicode scripts, blocks, categories and binary properties are written with
 * the \p and \P constructs as in Perl.
 * \p{prop} matches if
 * the input has the property prop, while \P{prop}
 * does not match if the input has that property.
 * 

 * Scripts, blocks, categories and binary properties can be used both inside
 * and outside of a character class.
 * 
 * 

 * Scripts are specified either with the prefix {@code Is}, as in
 * {@code IsHiragana}, or by using  the {@code script} keyword (or its short
 * form {@code sc})as in {@code script=Hiragana} or {@code sc=Hiragana}.
 * 

 * The script names supported by Pattern are the valid script names
 * accepted and defined by
 * {@link java.lang.Character.UnicodeScript#forName(String) UnicodeScript.forName}.
 * 
 * 

 * Blocks are specified with the prefix {@code In}, as in
 * {@code InMongolian}, or by using the keyword {@code block} (or its short
 * form {@code blk}) as in {@code block=Mongolian} or {@code blk=Mongolian}.
 * 

 * The block names supported by Pattern are the valid block names
 * accepted and defined by
 * {@link java.lang.Character.UnicodeBlock#forName(String) UnicodeBlock.forName}.
 * 

 * 
 * Categories may be specified with the optional prefix {@code Is}:
 * Both {@code \p{L}} and {@code \p{IsL}} denote the category of Unicode
 * letters. Same as scripts and blocks, categories can also be specified
 * by using the keyword {@code general_category} (or its short form
 * {@code gc}) as in {@code general_category=Lu} or {@code gc=Lu}.
 * 

 * The supported categories are those of
 * 
 * The Unicode Standard in the version specified by the
 * {@link java.lang.Character Character} class. The category names are those
 * defined in the Standard, both normative and informative.
 * 

 * 
 * Binary properties are specified with the prefix {@code Is}, as in
 * {@code IsAlphabetic}. The supported binary properties by Pattern
 * are
 * 

 *    Alphabetic
 *   
 Ideographic
 *   
 Letter
 *   
 Lowercase
 *   
 Uppercase
 *   
 Titlecase
 *   
 Punctuation
 *   
 Control
 *   
 White_Space
 *   
 Digit
 *   
 Hex_Digit
 *   
 Noncharacter_Code_Point
 *   
 Assigned
 * 



 * 
 * Predefined Character classes and POSIX character classes are in
 * conformance with the recommendation of Annex C: Compatibility Properties
 * of Unicode Regular Expression
 * .
 * 

 * 
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 *     
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 *     
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 *     
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 *     
 * 
 *     
 * Classes Matches
\p{Lower} A lowercase character:\p{IsLowercase}
\p{Upper} An uppercase character:\p{IsUppercase}
\p{ASCII} All ASCII:[\x00-\x7F]
\p{Alpha} An alphabetic character:\p{IsAlphabetic}
\p{Digit} A decimal digit character:p{IsDigit}
\p{Alnum} An alphanumeric character:[\p{IsAlphabetic}\p{IsDigit}]
\p{Punct} A punctuation character:p{IsPunctuation}
\p{Graph} A visible character: [^\p{IsWhite_Space}\p{gc=Cc}\p{gc=Cs}\p{gc=Cn}]
\p{Print} A printable character: [\p{Graph}\p{Blank}&&[^\p{Cntrl}]]
\p{Blank} A space or a tab: [\p{IsWhite_Space}&&[^\p{gc=Zl}\p{gc=Zp}\x0a\x0b\x0c\x0d\x85]]
\p{Cntrl} A control character: \p{gc=Cc}
\p{XDigit} A hexadecimal digit: [\p{gc=Nd}\p{IsHex_Digit}]
\p{Space} A whitespace character:\p{IsWhite_Space}
\d A digit: \p{IsDigit}
\D A non-digit: [^\d]
\s A whitespace character: \p{IsWhite_Space}
\S A non-whitespace character: [^\s]
\w A word character: [\p{Alpha}\p{gc=Mn}\p{gc=Me}\p{gc=Mc}\p{Digit}\p{gc=Pc}]
\W A non-word character: [^\w]
 * 

 * 
 * Categories that behave like the java.lang.Character
 * boolean ismethodname methods (except for the deprecated ones) are
 * available through the same \p{prop} syntax where
 * the specified property has the name javamethodname.
 *
 * 
 Comparison to Perl 5 

 *
 * The Pattern engine performs traditional NFA-based matching
 * with ordered alternation as occurs in Perl 5.
 *
 * 
 Perl constructs not supported by this class: 
 *
 * 
 *     Predefined character classes (Unicode character)
 *    
\h    A horizontal whitespace
 *    
\H    A non horizontal whitespace
 *    
\v    A vertical whitespace
 *    
\V    A non vertical whitespace
 *    
\R    Any Unicode linebreak sequence
 *    \u005cu000D\u005cu000A|[\u005cu000A\u005cu000B\u005cu000C\u005cu000D\u005cu0085\u005cu2028\u005cu2029]
 *    \X    Match Unicode
 *    
 *    extended grapheme cluster
 *    
 *
 *     The backreference constructs, \g{n} for
 *    the n^thcapturing group and
 *    \g{name} for
 *    named-capturing group.
 *    
 *
 *     The named character construct, \N{name}
 *    for a Unicode character by its name.
 *    
 *
 *     The conditional constructs
 *    (?(condition)X) and
 *    (?(condition)X|Y),
 *    
 *
 *     The embedded code constructs (?{code})
 *    and (??{code}),
 *
 *     The embedded comment syntax (?#comment), and 
 *
 *     The preprocessing operations \l \u,
 *    \L, and \U.  
 *
 * 
 *
 *  Constructs supported by this class but not by Perl: 
 *
 * 
 *
 *     Character-class union and intersection as described
 *    above.
 *
 * 
 *
 *  Notable differences from Perl: 
 *
 * 
 *
 *     In Perl, \1 through \9 are always interpreted
 *    as back references; a backslash-escaped number greater than 9 is
 *    treated as a back reference if at least that many subexpressions exist,
 *    otherwise it is interpreted, if possible, as an octal escape.  In this
 *    class octal escapes must always begin with a zero. In this class,
 *    \1 through \9 are always interpreted as back
 *    references, and a larger number is accepted as a back reference if at
 *    least that many subexpressions exist at that point in the regular
 *    expression, otherwise the parser will drop digits until the number is
 *    smaller or equal to the existing number of groups or it is one digit.
 *    
 *
 *     Perl uses the g flag to request a match that resumes
 *    where the last match left off.  This functionality is provided implicitly
 *    by the {@link Matcher} class: Repeated invocations of the {@link
 *    Matcher#find find} method will resume where the last match left off,
 *    unless the matcher is reset.  
 *
 *     In Perl, embedded flags at the top level of an expression affect
 *    the whole expression.  In this class, embedded flags always take effect
 *    at the point at which they appear, whether they are at the top level or
 *    within a group; in the latter case, flags are restored at the end of the
 *    group just as in Perl.  
 *
 * 
 *
 *
 *  For a more precise description of the behavior of regular expression
 * constructs, please see 
 * Mastering Regular Expressions, 3nd Edition, Jeffrey E. F. Friedl,
 * O'Reilly and Associates, 2006.
 * 
 *
 * @see java.lang.String#split(String, int)
 * @see java.lang.String#split(String)
 *
 * @author      Mike McCloskey
 * @author      Mark Reinhold
 * @author      JSR-51 Expert Group
 * @since       1.4
 * @spec        JSR-51
 */

public final class Pattern implements java.io.Serializable
{

    /**
     * Regular expression modifier values.  Instead of being passed as
     * arguments, they can also be passed as inline modifiers.
     * For example, the following statements have the same effect.
     *      * RegExp r1 = RegExp.compile("abc", Pattern.I|Pattern.M);
     * RegExp r2 = RegExp.compile("(?im)abc", 0);
     * 
     *
     * The flags are duplicated so that the familiar Perl match flag
     * names are available.
     */

    /**
     * Enables Unix lines mode.
     *
     *  In this mode, only the '\n' line terminator is recognized
     * in the behavior of ., ^, and $.
     *
     * 
 Unix lines mode can also be enabled via the embedded flag
     * expression (?d).
     */
    public static final int UNIX_LINES = 0x01;

    /**
     * Enables case-insensitive matching.
     *
     * 
 By default, case-insensitive matching assumes that only characters
     * in the US-ASCII charset are being matched.  Unicode-aware
     * case-insensitive matching can be enabled by specifying the {@link
     * #UNICODE_CASE} flag in conjunction with this flag.
     *
     * 
 Case-insensitive matching can also be enabled via the embedded flag
     * expression (?i).
     *
     * 
 Specifying this flag may impose a slight performance penalty.  
     */
    public static final int CASE_INSENSITIVE = 0x02;

    /**
     * Permits whitespace and comments in pattern.
     *
     *  In this mode, whitespace is ignored, and embedded comments starting
     * with # are ignored until the end of a line.
     *
     * 
 Comments mode can also be enabled via the embedded flag
     * expression (?x).
     */
    public static final int COMMENTS = 0x04;

    /**
     * Enables multiline mode.
     *
     * 
 In multiline mode the expressions ^ and $ match
     * just after or just before, respectively, a line terminator or the end of
     * the input sequence.  By default these expressions only match at the
     * beginning and the end of the entire input sequence.
     *
     * 
 Multiline mode can also be enabled via the embedded flag
     * expression (?m).  
     */
    public static final int MULTILINE = 0x08;

    /**
     * Enables literal parsing of the pattern.
     *
     *  When this flag is specified then the input string that specifies
     * the pattern is treated as a sequence of literal characters.
     * Metacharacters or escape sequences in the input sequence will be
     * given no special meaning.
     *
     * 
The flags CASE_INSENSITIVE and UNICODE_CASE retain their impact on
     * matching when used in conjunction with this flag. The other flags
     * become superfluous.
     *
     * 
 There is no embedded flag character for enabling literal parsing.
     * @since 1.5
     */
    public static final int LITERAL = 0x10;

    /**
     * Enables dotall mode.
     *
     * 
 In dotall mode, the expression . matches any character,
     * including a line terminator.  By default this expression does not match
     * line terminators.
     *
     * 
 Dotall mode can also be enabled via the embedded flag
     * expression (?s).  (The s is a mnemonic for
     * "single-line" mode, which is what this is called in Perl.)  
     */
    public static final int DOTALL = 0x20;

    /**
     * Enables Unicode-aware case folding.
     *
     *  When this flag is specified then case-insensitive matching, when
     * enabled by the {@link #CASE_INSENSITIVE} flag, is done in a manner
     * consistent with the Unicode Standard.  By default, case-insensitive
     * matching assumes that only characters in the US-ASCII charset are being
     * matched.
     *
     * 
 Unicode-aware case folding can also be enabled via the embedded flag
     * expression (?u).
     *
     * 
 Specifying this flag may impose a performance penalty.  
     */
    public static final int UNICODE_CASE = 0x40;

    /**
     * Enables canonical equivalence.
     *
     *  When this flag is specified then two characters will be considered
     * to match if, and only if, their full canonical decompositions match.
     * The expression "a\u030A", for example, will match the
     * string "\u00E5" when this flag is specified.  By default,
     * matching does not take canonical equivalence into account.
     *
     * 
 There is no embedded flag character for enabling canonical
     * equivalence.
     *
     * 
 Specifying this flag may impose a performance penalty.  
     */
    public static final int CANON_EQ = 0x80;

    /**
     * Enables the Unicode version of Predefined character classes and
     * POSIX character classes as eefined by Unicode Technical
     * Standard #18: Unicode Regular Expression
     * Annex C: Compatibility Properties.
     * 
     *
     * This flag has no effect on Android, unicode character classes are always
     * used.
     *
     * @since 1.7
     */
    public static final int UNICODE_CHARACTER_CLASS = 0x100;

    /* Pattern has only two serialized components: The pattern string
     * and the flags, which are all that is needed to recompile the pattern
     * when it is deserialized.
     */

    /** use serialVersionUID from Merlin b59 for interoperability */
    private static final long serialVersionUID = 5073258162644648461L;

    /**
     * The original regular-expression pattern string.
     *
     * @serial
     */
    private final String pattern;

    /**
     * The original pattern flags.
     *
     * @serial
     */
    private final int flags;

    transient long address;

    private static final NativeAllocationRegistry registry = new NativeAllocationRegistry(
            Pattern.class.getClassLoader(), getNativeFinalizer(), nativeSize());


    /**
     * Compiles the given regular expression into a pattern.  
     *
     * @param  regex
     *         The expression to be compiled
     *
     * @throws  PatternSyntaxException
     *          If the expression's syntax is invalid
     */
    public static Pattern compile(String regex) {
        return new Pattern(regex, 0);
    }

    /**
     * Compiles the given regular expression into a pattern with the given
     * flags.  
     *
     * @param  regex
     *         The expression to be compiled
     *
     * @param  flags
     *         Match flags, a bit mask that may include
     *         {@link #CASE_INSENSITIVE}, {@link #MULTILINE}, {@link #DOTALL},
     *         {@link #UNICODE_CASE}, {@link #CANON_EQ}, {@link #UNIX_LINES},
     *         {@link #LITERAL}, {@link #UNICODE_CHARACTER_CLASS}
     *         and {@link #COMMENTS}
     *
     * @throws  IllegalArgumentException
     *          If bit values other than those corresponding to the defined
     *          match flags are set in flags
     *
     * @throws  PatternSyntaxException
     *          If the expression's syntax is invalid
     */
    public static Pattern compile(String regex, int flags) throws PatternSyntaxException {
        return new Pattern(regex, flags);
    }

    /**
     * Returns the regular expression from which this pattern was compiled.
     * 
     *
     * @return  The source of this pattern
     */
    public String pattern() {
        return pattern;
    }

    /**
     * Returns the string representation of this pattern. This
     * is the regular expression from which this pattern was
     * compiled.
     *
     * @return  The string representation of this pattern
     * @since 1.5
     */
    public String toString() {
        return pattern;
    }

    /**
     * Creates a matcher that will match the given input against this pattern.
     * 
     *
     * @param  input
     *         The character sequence to be matched
     *
     * @return  A new matcher for this pattern
     */
    public Matcher matcher(CharSequence input) {
        Matcher m = new Matcher(this, input);
        return m;
    }

    /**
     * Returns this pattern's match flags.  
     *
     * @return  The match flags specified when this pattern was compiled
     */
    public int flags() {
        return flags;
    }

    /**
     * Compiles the given regular expression and attempts to match the given
     * input against it.
     *
     *  An invocation of this convenience method of the form
     *
     * 
     * Pattern.matches(regex, input);
     *
     * behaves in exactly the same way as the expression
     *
     *      * Pattern.compile(regex).matcher(input).matches()
     *
     *  If a pattern is to be used multiple times, compiling it once and reusing
     * it will be more efficient than invoking this method each time.  
     *
     * @param  regex
     *         The expression to be compiled
     *
     * @param  input
     *         The character sequence to be matched
     *
     * @throws  PatternSyntaxException
     *          If the expression's syntax is invalid
     */
    public static boolean matches(String regex, CharSequence input) {
        Pattern p = Pattern.compile(regex);
        Matcher m = p.matcher(input);
        return m.matches();
    }

    /**
     * Splits the given input sequence around matches of this pattern.
     *
     *  The array returned by this method contains each substring of the
     * input sequence that is terminated by another subsequence that matches
     * this pattern or is terminated by the end of the input sequence.  The
     * substrings in the array are in the order in which they occur in the
     * input.  If this pattern does not match any subsequence of the input then
     * the resulting array has just one element, namely the input sequence in
     * string form.
     *
     * 
 The limit parameter controls the number of times the
     * pattern is applied and therefore affects the length of the resulting
     * array.  If the limit n is greater than zero then the pattern
     * will be applied at most n - 1 times, the array's
     * length will be no greater than n, and the array's last entry
     * will contain all input beyond the last matched delimiter.  If n
     * is non-positive then the pattern will be applied as many times as
     * possible and the array can have any length.  If n is zero then
     * the pattern will be applied as many times as possible, the array can
     * have any length, and trailing empty strings will be discarded.
     *
     * 
 The input "boo:and:foo", for example, yields the following
     * results with these parameters:
     *
     * 

     * 
     *     
     *     
     * 
     *     
     *     
     * 
     *     
     *     
     * 
     *     
     *     
     * 
     *     
     *     
     * 
     *     
     *     
     * 
     *     
     *     
     * Regex     Limit     Result    
: 2 { "boo", "and:foo" }
: 5 { "boo", "and", "foo" }
: -2 { "boo", "and", "foo" }
o 5 { "b", "", ":and:f", "", "" }
o -2 { "b", "", ":and:f", "", "" }
o 0 { "b", "", ":and:f" }
     *
     *
     * @param  input
     *         The character sequence to be split
     *
     * @param  limit
     *         The result threshold, as described above
     *
     * @return  The array of strings computed by splitting the input
     *          around matches of this pattern
     */
    public String[] split(CharSequence input, int limit) {
        String[] fast = fastSplit(pattern, input.toString(), limit);
        if (fast != null) {
            return fast;
        }

        int index = 0;
        boolean matchLimited = limit > 0;
        ArrayList matchList = new ArrayList<>();
        Matcher m = matcher(input);

        // Add segments before each match found
        while(m.find()) {
            if (!matchLimited || matchList.size() < limit - 1) {
                String match = input.subSequence(index, m.start()).toString();
                matchList.add(match);
                index = m.end();
            } else if (matchList.size() == limit - 1) { // last one
                String match = input.subSequence(index,
                                                 input.length()).toString();
                matchList.add(match);
                index = m.end();
            }
        }

        // If no match was found, return this
        if (index == 0)
            return new String[] {input.toString()};

        // Add remaining segment
        if (!matchLimited || matchList.size() < limit)
            matchList.add(input.subSequence(index, input.length()).toString());

        // Construct result
        int resultSize = matchList.size();
        if (limit == 0)
            while (resultSize > 0 && matchList.get(resultSize-1).equals(""))
                resultSize--;
        String[] result = new String[resultSize];
        return matchList.subList(0, resultSize).toArray(result);
    }

    private static final String FASTSPLIT_METACHARACTERS = "\\?*+[](){}^$.|";

    /**
     * Returns a result equivalent to {@code s.split(separator, limit)} if it's able
     * to compute it more cheaply than native impl, or null if the caller should fall back to
     * using native impl.
     *
     *  fastpath will work  if the regex is a
     *   (1)one-char String and this character is not one of the
     *      RegEx's meta characters ".$|()[{^?*+\\", or
     *   (2)two-char String and the first char is the backslash and
     *      the second is one of regEx's meta characters ".$|()[{^?*+\\".
     * @hide
     */
    public static String[] fastSplit(String re, String input, int limit) {
        // Can we do it cheaply?
        int len = re.length();
        if (len == 0) {
            return null;
        }
        char ch = re.charAt(0);
        if (len == 1 && FASTSPLIT_METACHARACTERS.indexOf(ch) == -1) {
            // We're looking for a single non-metacharacter. Easy.
        } else if (len == 2 && ch == '\\') {
            // We're looking for a quoted character.
            // Quoted metacharacters are effectively single non-metacharacters.
            ch = re.charAt(1);
            if (FASTSPLIT_METACHARACTERS.indexOf(ch) == -1) {
                return null;
            }
        } else {
            return null;
        }

        // We can do this cheaply...

        // Unlike Perl, which considers the result of splitting the empty string to be the empty
        // array, Java returns an array containing the empty string.
        if (input.isEmpty()) {
            return new String[] { "" };
        }

        // Count separators
        int separatorCount = 0;
        int begin = 0;
        int end;
        while (separatorCount + 1 != limit && (end = input.indexOf(ch, begin)) != -1) {
            ++separatorCount;
            begin = end + 1;
        }
        int lastPartEnd = input.length();
        if (limit == 0 && begin == lastPartEnd) {
            // Last part is empty for limit == 0, remove all trailing empty matches.
            if (separatorCount == lastPartEnd) {
                // Input contains only separators.
                return EmptyArray.STRING;
            }
            // Find the beginning of trailing separators.
            do {
                --begin;
            } while (input.charAt(begin - 1) == ch);
            // Reduce separatorCount and fix lastPartEnd.
            separatorCount -= input.length() - begin;
            lastPartEnd = begin;
        }

        // Collect the result parts.
        String[] result = new String[separatorCount + 1];
        begin = 0;
        for (int i = 0; i != separatorCount; ++i) {
            end = input.indexOf(ch, begin);
            result[i] = input.substring(begin, end);
            begin = end + 1;
        }
        // Add last part.
        result[separatorCount] = input.substring(begin, lastPartEnd);
        return result;
    }

    /**
     * Splits the given input sequence around matches of this pattern.
     *
     *  This method works as if by invoking the two-argument {@link
     * #split(java.lang.CharSequence, int) split} method with the given input
     * sequence and a limit argument of zero.  Trailing empty strings are
     * therefore not included in the resulting array. 
     *
     *  The input "boo:and:foo", for example, yields the following
     * results with these expressions:
     *
     * 

     * 
     *     
     * 
     *     
     * 
     *     
     * Regex     Result
: { "boo", "and", "foo" }
o { "b", "", ":and:f" }
     *
     *
     * @param  input
     *         The character sequence to be split
     *
     * @return  The array of strings computed by splitting the input
     *          around matches of this pattern
     */
    public String[] split(CharSequence input) {
        return split(input, 0);
    }

    /**
     * Returns a literal pattern String for the specified
     * String.
     *
     * This method produces a String that can be used to
     * create a Pattern that would match the string
     * s as if it were a literal pattern. Metacharacters
     * or escape sequences in the input sequence will be given no special
     * meaning.
     *
     * @param  s The string to be literalized
     * @return  A literal string replacement
     * @since 1.5
     */
    public static String quote(String s) {
        int slashEIndex = s.indexOf("\\E");
        if (slashEIndex == -1)
            return "\\Q" + s + "\\E";

        StringBuilder sb = new StringBuilder(s.length() * 2);
        sb.append("\\Q");
        slashEIndex = 0;
        int current = 0;
        while ((slashEIndex = s.indexOf("\\E", current)) != -1) {
            sb.append(s.substring(current, slashEIndex));
            current = slashEIndex + 2;
            sb.append("\\E\\\\E\\Q");
        }
        sb.append(s.substring(current, s.length()));
        sb.append("\\E");
        return sb.toString();
    }

    /**
     * Recompile the Pattern instance from a stream.  The original pattern
     * string is read in and the object tree is recompiled from it.
     */
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {

        // Read in all fields
        s.defaultReadObject();
        compile();
    }

    /**
     * This private constructor is used to create all Patterns. The pattern
     * string and match flags are all that is needed to completely describe
     * a Pattern.
     */
    private Pattern(String p, int f) {
        if ((f & CANON_EQ) != 0) {
            throw new UnsupportedOperationException("CANON_EQ flag not supported");
        }
        int supportedFlags = CASE_INSENSITIVE | COMMENTS | DOTALL | LITERAL | MULTILINE | UNICODE_CASE | UNIX_LINES;
        if ((f & ~supportedFlags) != 0) {
            throw new IllegalArgumentException("Unsupported flags: " + (f & ~supportedFlags));
        }
        this.pattern = p;
        this.flags = f;
        compile();
    }

    private void compile() throws PatternSyntaxException {
        if (pattern == null) {
            throw new NullPointerException("pattern == null");
        }

        String icuPattern = pattern;
        if ((flags & LITERAL) != 0) {
            icuPattern = quote(pattern);
        }

        // These are the flags natively supported by ICU.
        // They even have the same value in native code.
        int icuFlags = flags & (CASE_INSENSITIVE | COMMENTS | MULTILINE | DOTALL | UNIX_LINES);
        address = compileImpl(icuPattern, icuFlags);
        registry.registerNativeAllocation(this, address);
    }

    private static native long compileImpl(String regex, int flags);
    private static native long getNativeFinalizer();
    private static native int nativeSize();

    /**
     * Creates a predicate which can be used to match a string.
     *
     * @return  The predicate which can be used for matching on a string
     * @since   1.8
     */
    public Predicate asPredicate() {
        return s -> matcher(s).find();
    }

    /**
     * Creates a stream from the given input sequence around matches of this
     * pattern.
     *
     *  The stream returned by this method contains each substring of the
     * input sequence that is terminated by another subsequence that matches
     * this pattern or is terminated by the end of the input sequence.  The
     * substrings in the stream are in the order in which they occur in the
     * input. Trailing empty strings will be discarded and not encountered in
     * the stream.
     *
     * 
 If this pattern does not match any subsequence of the input then
     * the resulting stream has just one element, namely the input sequence in
     * string form.
     *
     * 
 When there is a positive-width match at the beginning of the input
     * sequence then an empty leading substring is included at the beginning
     * of the stream. A zero-width match at the beginning however never produces
     * such empty leading substring.
     *
     * 
 If the input sequence is mutable, it must remain constant during the
     * execution of the terminal stream operation.  Otherwise, the result of the
     * terminal stream operation is undefined.
     *
     * @param   input
     *          The character sequence to be split
     *
     * @return  The stream of strings computed by splitting the input
     *          around matches of this pattern
     * @see     #split(CharSequence)
     * @since   1.8
     */
    public Stream splitAsStream(final CharSequence input) {
        class MatcherIterator implements Iterator {
            private final Matcher matcher;
            // The start position of the next sub-sequence of input
            // when current == input.length there are no more elements
            private int current;
            // null if the next element, if any, needs to obtained
            private String nextElement;
            // > 0 if there are N next empty elements
            private int emptyElementCount;

            MatcherIterator() {
                this.matcher = matcher(input);
            }

            public String next() {
                if (!hasNext())
                    throw new NoSuchElementException();

                if (emptyElementCount == 0) {
                    String n = nextElement;
                    nextElement = null;
                    return n;
                } else {
                    emptyElementCount--;
                    return "";
                }
            }

            public boolean hasNext() {
                if (nextElement != null || emptyElementCount > 0)
                    return true;

                if (current == input.length())
                    return false;

                // Consume the next matching element
                // Count sequence of matching empty elements
                while (matcher.find()) {
                    nextElement = input.subSequence(current, matcher.start()).toString();
                    current = matcher.end();
                    if (!nextElement.isEmpty()) {
                        return true;
                    } else if (current > 0) { // no empty leading substring for zero-width
                                              // match at the beginning of the input
                        emptyElementCount++;
                    }
                }

                // Consume last matching element
                nextElement = input.subSequence(current, input.length()).toString();
                current = input.length();
                if (!nextElement.isEmpty()) {
                    return true;
                } else {
                    // Ignore a terminal sequence of matching empty elements
                    emptyElementCount = 0;
                    nextElement = null;
                    return false;
                }
            }
        }
        return StreamSupport.stream(Spliterators.spliteratorUnknownSize(
                new MatcherIterator(), Spliterator.ORDERED | Spliterator.NONNULL), false);
    }
}

Construct	Matches

Characters
x	The character x
`\\`	The backslash character
`\0`n	The character with octal value `0`n * (0 `<=` n `<=` 7)
`\0`nn	The character with octal value `0`nn * (0 `<=` n `<=` 7)
`\0`mnn	The character with octal value `0`mnn * (0 `<=` m `<=` 3, * 0 `<=` n `<=` 7)
`\x`hh	The character with hexadecimal value `0x`hh
`\u`hhhh	The character with hexadecimal value `0x`hhhh
`\x`{h...h}	The character with hexadecimal value `0x`h...h * ({@link java.lang.Character#MIN_CODE_POINT Character.MIN_CODE_POINT} * <= `0x`h...h <= * {@link java.lang.Character#MAX_CODE_POINT Character.MAX_CODE_POINT})
`\t`	The tab character (`'\u0009'`)
`\n`	The newline (line feed) character (`'\u000A'`)
`\r`	The carriage-return character (`'\u000D'`)
`\f`	The form-feed character (`'\u000C'`)
`\a`	The alert (bell) character (`'\u0007'`)
`\e`	The escape character (`'\u001B'`)
`\c`x	The control character corresponding to x

Character classes
`[abc]`	`a`, `b`, or `c` (simple class)
`[^abc]`	Any character except `a`, `b`, or `c` (negation)
`[a-zA-Z]`	`a` through `z` * or `A` through `Z`, inclusive (range)
`[a-d[m-p]]`	`a` through `d`, * or `m` through `p`: `[a-dm-p]` (union)
`[a-z&&[def]]`	`d`, `e`, or `f` (intersection)
`[a-z&&[^bc]]`	`a` through `z`, * except for `b` and `c`: `[ad-z]` (subtraction)
`[a-z&&[^m-p]]`	`a` through `z`, * and not `m` through `p`: `[a-lq-z]`(subtraction)

Predefined character classes
`.`	Any character (may or may not match line terminators)
`\d`	A digit: `[0-9]`
`\D`	A non-digit: `[^0-9]`
`\s`	A whitespace character: `[ \t\n\x0B\f\r]`
`\S`	A non-whitespace character: `[^\s]`
`\w`	A word character: `[a-zA-Z_0-9]`
`\W`	A non-word character: `[^\w]`

POSIX character classes (US-ASCII only)
`\p{Lower}`	A lower-case alphabetic character: `[a-z]`
`\p{Upper}`	An upper-case alphabetic character:`[A-Z]`
`\p{ASCII}`	All ASCII:`[\x00-\x7F]`
`\p{Alpha}`	An alphabetic character:`[\p{Lower}\p{Upper}]`
`\p{Digit}`	A decimal digit: `[0-9]`
`\p{Alnum}`	An alphanumeric character:`[\p{Alpha}\p{Digit}]`
`\p{Punct}`	Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{\|}~
`\p{Graph}`	A visible character: `[\p{Alnum}\p{Punct}]`
`\p{Print}`	A printable character: `[\p{Graph}\x20]`
`\p{Blank}`	A space or a tab: `[ \t]`
`\p{Cntrl}`	A control character: `[\x00-\x1F\x7F]`
`\p{XDigit}`	A hexadecimal digit: `[0-9a-fA-F]`
`\p{Space}`	A whitespace character: `[ \t\n\x0B\f\r]`

java.lang.Character classes (simple java character type)
`\p{javaLowerCase}`	Equivalent to java.lang.Character.isLowerCase()
`\p{javaUpperCase}`	Equivalent to java.lang.Character.isUpperCase()
`\p{javaWhitespace}`	Equivalent to java.lang.Character.isWhitespace()
`\p{javaMirrored}`	Equivalent to java.lang.Character.isMirrored()

Classes for Unicode scripts, blocks, categories and binary properties
`\p{IsLatin}`	A Latin script character (script)
`\p{InGreek}`	A character in the Greek block (block)
`\p{Lu}`	An uppercase letter (category)
`\p{IsAlphabetic}`	An alphabetic character (binary property)
`\p{Sc}`	A currency symbol
`\P{InGreek}`	Any character except one in the Greek block (negation)
`[\p{L}&&[^\p{Lu}]]`	Any letter except an uppercase letter (subtraction)

Boundary matchers
`^`	The beginning of a line
`$`	The end of a line
`\b`	A word boundary
`\B`	A non-word boundary
`\A`	The beginning of the input
`\G`	The end of the previous match
`\Z`	The end of the input but for the final * terminator, if any
`\z`	The end of the input

Greedy quantifiers
X`?`	X, once or not at all
X`*`	X, zero or more times
X`+`	X, one or more times
X`{`n`}`	X, exactly n times
X`{`n`,}`	X, at least n times
X`{`n`,`m`}`	X, at least n but not more than m times

Reluctant quantifiers
X`??`	X, once or not at all
X`*?`	X, zero or more times
X`+?`	X, one or more times
X`{`n`}?`	X, exactly n times
X`{`n`,}?`	X, at least n times
X`{`n`,`m`}?`	X, at least n but not more than m times

Possessive quantifiers
X`?+`	X, once or not at all
X`*+`	X, zero or more times
X`++`	X, one or more times
X`{`n`}+`	X, exactly n times
X`{`n`,}+`	X, at least n times
X`{`n`,`m`}+`	X, at least n but not more than m times

Logical operators
XY	X followed by Y
X`\|`Y	Either X or Y
`(`X`)`	X, as a capturing group

Back references
`\`n	Whatever the n^th * capturing group matched
`\`k<name>	Whatever the * named-capturing group "name" matched

Quotation
`\`	Nothing, but quotes the following character
`\Q`	Nothing, but quotes all characters until `\E`
`\E`	Nothing, but ends quoting started by `\Q`

Special constructs (named-capturing and non-capturing)
`(?<name>`X`)`	X, as a named-capturing group
`(?:`X`)`	X, as a non-capturing group
`(?idmsuxU-idmsuxU)`	Nothing, but turns match flags i * d m s * u x U * on - off
`(?idmsux-idmsux:`X`)`	X, as a non-capturing group with the * given flags i d * m s u * x on - off
`(?=`X`)`	X, via zero-width positive lookahead
`(?!`X`)`	X, via zero-width negative lookahead
`(?<=`X`)`	X, via zero-width positive lookbehind
`(?<!`X`)`	X, via zero-width negative lookbehind
`(?>`X`)`	X, as an independent, non-capturing group

1	`((A)(B(C)))`
2	`(A)`
3	`(B(C))`
4	`(C)`

Classes	Matches
`\p{Lower}`	A lowercase character:`\p{IsLowercase}`
`\p{Upper}`	An uppercase character:`\p{IsUppercase}`
`\p{ASCII}`	All ASCII:`[\x00-\x7F]`
`\p{Alpha}`	An alphabetic character:`\p{IsAlphabetic}`
`\p{Digit}`	A decimal digit character:`p{IsDigit}`
`\p{Alnum}`	An alphanumeric character:`[\p{IsAlphabetic}\p{IsDigit}]`
`\p{Punct}`	A punctuation character:`p{IsPunctuation}`
`\p{Graph}`	A visible character: `[^\p{IsWhite_Space}\p{gc=Cc}\p{gc=Cs}\p{gc=Cn}]`
`\p{Print}`	A printable character: `[\p{Graph}\p{Blank}&&[^\p{Cntrl}]]`
`\p{Blank}`	A space or a tab: `[\p{IsWhite_Space}&&[^\p{gc=Zl}\p{gc=Zp}\x0a\x0b\x0c\x0d\x85]]`
`\p{Cntrl}`	A control character: `\p{gc=Cc}`
`\p{XDigit}`	A hexadecimal digit: `[\p{gc=Nd}\p{IsHex_Digit}]`
`\p{Space}`	A whitespace character:`\p{IsWhite_Space}`
`\d`	A digit: `\p{IsDigit}`
`\D`	A non-digit: `[^\d]`
`\s`	A whitespace character: `\p{IsWhite_Space}`
`\S`	A non-whitespace character: `[^\s]`
`\w`	A word character: `[\p{Alpha}\p{gc=Mn}\p{gc=Me}\p{gc=Mc}\p{Digit}\p{gc=Pc}]`
`\W`	A non-word character: `[^\w]`

Regex	Limit	Result
:	2	`{ "boo", "and:foo" }`
:	5	`{ "boo", "and", "foo" }`
:	-2	`{ "boo", "and", "foo" }`
o	5	`{ "b", "", ":and:f", "", "" }`
o	-2	`{ "b", "", ":and:f", "", "" }`
o	0	`{ "b", "", ":and:f" }`

Regex	Result
:	`{ "boo", "and", "foo" }`
o	`{ "b", "", ":and:f" }`

1	Literal escape	`\x`
2	Grouping	`[...]`
3	Range	`a-z`
4	Union	`[a-e][i-u]`
5	Intersection	`[a-z&&[aeiou]]`