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diff --git a/doc/SYNTAX.md b/doc/SYNTAX.md new file mode 100644 index 0000000..449f262 --- /dev/null +++ b/doc/SYNTAX.md @@ -0,0 +1,1069 @@ + +# Oniguruma syntax (operator) configuration + +_Documented for Oniguruma 6.9.2 (2019/03/28)_ + + +---------- + + +## Overview + +This document details how to configure Oniguruma's syntax, by describing the desired +syntax operators and behaviors in an instance of the OnigSyntaxType struct, just like +the built-in Oniguruma syntaxes do. + +Configuration operators are bit flags, and are broken into multiple groups, somewhat arbitrarily, +because Oniguruma takes its configuration as a trio of 32-bit `unsigned int` values, assigned as +the first three fields in an `OnigSyntaxType` struct: + +```C +typedef struct { + unsigned int op; + unsigned int op2; + unsigned int behavior; + OnigOptionType options; /* default option */ + OnigMetaCharTableType meta_char_table; +} OnigSyntaxType; +``` + +The first group of configuration flags (`op`) roughly corresponds to the +configuration for "basic regex." The second group (`op2`) roughly corresponds +to the configuration for "advanced regex." And the third group (`behavior`) +describes more-or-less what to do for broken input, bad input, or other corner-case +regular expressions whose meaning is not well-defined. These three groups of +flags are described in full below, and tables of their usages for various syntaxes +follow. + +The `options` field describes the default compile options to use if the caller does +not specify any options when invoking `onig_new()`. + +The `meta_char_table` field is used exclusively by the ONIG_SYN_OP_VARIABLE_META_CHARACTERS +option, which allows the various regex metacharacters, like `*` and `?`, to be replaced +with alternates (for example, SQL typically uses `%` instead of `.*` and `_` instead of `?`). + + +---------- + + +## Group One Flags (op) + + +This group contains "basic regex" constructs, features common to most regex systems. + + +### 0. ONIG_SYN_OP_VARIABLE_META_CHARACTERS + +_Set in: none_ + +Enables support for `onig_set_meta_char()`, which allows you to provide alternate +characters that will be used instead of the six special characters that are normally +these characters below: + + - `ONIG_META_CHAR_ESCAPE`: `\` + - `ONIG_META_CHAR_ANYCHAR`: `.` + - `ONIG_META_CHAR_ANYTIME`: `*` + - `ONIG_META_CHAR_ZERO_OR_ONE_TIME`: `?` + - `ONIG_META_CHAR_ONE_OR_MORE_TIME`: `+` + - `ONIG_META_CHAR_ANYCHAR_ANYTIME`: Equivalent in normal regex to `.*`, but supported + explicitly so that Oniguruma can support matching SQL `%` wildcards or shell `*` wildcards. + +If this flag is set, then the values defined using `onig_set_meta_char()` will be used; +if this flag is clear, then the default regex characters will be used instead, and +data set by `onig_set_meta_char()` will be ignored. + + +### 1. ONIG_SYN_OP_DOT_ANYCHAR (enable `.`) + +_Set in: PosixBasic, PosixExtended, Emacs, Grep, GnuRegex, Java, Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for the standard `.` metacharacter, meaning "any one character." You +usually want this flag on unless you have turned on `ONIG_SYN_OP_VARIABLE_META_CHARACTERS` +so that you can use a metacharacter other than `.` instead. + + +### 2. ONIG_SYN_OP_ASTERISK_ZERO_INF (enable `r*`) + +_Set in: PosixBasic, PosixExtended, Emacs, Grep, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the standard `r*` metacharacter, meaning "zero or more r's." +You usually want this flag set unless you have turned on `ONIG_SYN_OP_VARIABLE_META_CHARACTERS` +so that you can use a metacharacter other than `*` instead. + + +### 3. ONIG_SYN_OP_ESC_ASTERISK_ZERO_INF (enable `r\*`) + +_Set in: none_ + +Enables support for an escaped `r\*` metacharacter, meaning "zero or more r's." This is +useful if you have disabled support for the normal `r*` metacharacter because you want `*` +to simply match a literal `*` character, but you still want some way of activating "zero or more" +behavior. + + +### 4. ONIG_SYN_OP_PLUS_ONE_INF (enable `r+`) + +_Set in: PosixExtended, Emacs, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the standard `r+` metacharacter, meaning "one or more r's." +You usually want this flag set unless you have turned on `ONIG_SYN_OP_VARIABLE_META_CHARACTERS` +so that you can use a metacharacter other than `+` instead. + + +### 5. ONIG_SYN_OP_ESC_PLUS_ONE_INF (enable `r\+`) + +_Set in: Grep_ + +Enables support for an escaped `r\+` metacharacter, meaning "one or more r's." This is +useful if you have disabled support for the normal `r+` metacharacter because you want `+` +to simply match a literal `+` character, but you still want some way of activating "one or more" +behavior. + + +### 6. ONIG_SYN_OP_QMARK_ZERO_ONE (enable `r?`) + +_Set in: PosixExtended, Emacs, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the standard `r?` metacharacter, meaning "zero or one r" or "an optional r." +You usually want this flag set unless you have turned on `ONIG_SYN_OP_VARIABLE_META_CHARACTERS` +so that you can use a metacharacter other than `?` instead. + + +### 7. ONIG_SYN_OP_ESC_QMARK_ZERO_ONE (enable `r\?`) + +_Set in: Grep_ + +Enables support for an escaped `r\?` metacharacter, meaning "zero or one r" or "an optional +r." This is useful if you have disabled support for the normal `r?` metacharacter because +you want `?` to simply match a literal `?` character, but you still want some way of activating +"optional" behavior. + + +### 8. ONIG_SYN_OP_BRACE_INTERVAL (enable `r{l,u}`) + +_Set in: PosixExtended, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the `r{lower,upper}` range form, common to more advanced +regex engines, which lets you specify precisely a minimum and maximum range on how many r's +must match (and not simply "zero or more"). + +This form also allows `r{count}` to specify a precise count of r's that must match. + +This form also allows `r{lower,}` to be equivalent to `r{lower,infinity}`. + +If and only if the `ONIG_SYN_ALLOW_INTERVAL_LOW_ABBREV` behavior flag is set, +this form also allows `r{,upper}` to be equivalent to `r{0,upper}`; otherwise, +`r{,upper}` will be treated as an error. + + +### 9. ONIG_SYN_OP_ESC_BRACE_INTERVAL (enable `\{` and `\}`) + +_Set in: PosixBasic, Emacs, Grep_ + +Enables support for an escaped `r\{lower,upper\}` range form. This is useful if you +have disabled support for the normal `r{...}` range form and want curly braces to simply +match literal curly brace characters, but you still want some way of activating +"range" behavior. + + +### 10. ONIG_SYN_OP_VBAR_ALT (enable `r|s`) + +_Set in: PosixExtended, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the common `r|s` alternation operator. You usually want this +flag set. + + +### 11. ONIG_SYN_OP_ESC_VBAR_ALT (enable `\|`) + +_Set in: Emacs, Grep_ + +Enables support for an escaped `r\|s` alternation form. This is useful if you +have disabled support for the normal `r|s` alternation form and want `|` to simply +match a literal `|` character, but you still want some way of activating "alternate" behavior. + + +### 12. ONIG_SYN_OP_LPAREN_SUBEXP (enable `(r)`) + +_Set in: PosixExtended, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the common `(...)` grouping-and-capturing operators. You usually +want this flag set. + + +### 13. ONIG_SYN_OP_ESC_LPAREN_SUBEXP (enable `\(` and `\)`) + +_Set in: PosixBasic, Emacs, Grep_ + +Enables support for escaped `\(...\)` grouping-and-capturing operators. This is useful if you +have disabled support for the normal `(...)` grouping-and-capturing operators and want +parentheses to simply match literal parenthesis characters, but you still want some way of +activating "grouping" or "capturing" behavior. + + +### 14. ONIG_SYN_OP_ESC_AZ_BUF_ANCHOR (enable `\A` and `\Z` and `\z`) + +_Set in: GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the anchors `\A` (start-of-string), `\Z` (end-of-string or +newline-at-end-of-string), and `\z` (end-of-string) escapes. + +(If the escape metacharacter has been changed from the default of `\`, this +option will recognize that metacharacter instead.) + + +### 15. ONIG_SYN_OP_ESC_CAPITAL_G_BEGIN_ANCHOR (enable `\G`) + +_Set in: GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the special anchor `\G` (start-of-previous-match). + +(If the escape metacharacter has been changed from the default of `\`, this +option will recognize that metacharacter instead.) + +Note that `OnigRegex`/`regex_t` are not stateful objects, and do _not_ record +the location of the previous match. The `\G` flag uses the `start` parameter +explicitly passed to `onig_search()` (or `onig_search_with_param()` to determine +the "start of the previous match," so if the caller always passes the start of +the entire buffer as the function's `start` parameter, then `\G` will behave +exactly the same as `\A`. + + +### 16. ONIG_SYN_OP_DECIMAL_BACKREF (enable `\num`) + +_Set in: PosixBasic, PosixExtended, Emacs, Grep, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for subsequent matches to back references to prior capture groups `(...)` using +the common `\num` syntax (like `\3`). + +If this flag is clear, then a numeric escape like `\3` will either be treated as a literal `3`, +or, if `ONIG_SYN_OP_ESC_OCTAL3` is set, will be treated as an octal character code `\3`. + +You usually want this enabled, and it is enabled by default in every built-in syntax. + + +### 17. ONIG_SYN_OP_BRACKET_CC (enable `[...]`) + +_Set in: PosixBasic, PosixExtended, Emacs, Grep, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for recognizing character classes, like `[a-z]`. If this flag is not set, `[` +and `]` will be treated as ordinary literal characters instead of as metacharacters. + +You usually want this enabled, and it is enabled by default in every built-in syntax. + + +### 18. ONIG_SYN_OP_ESC_W_WORD (enable `\w` and `\W`) + +_Set in: Grep, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the common `\w` and `\W` shorthand forms. These match "word characters," +whose meaning varies depending on the encoding being used. + +In ASCII encoding, `\w` is equivalent to `[A-Za-z0-9_]`. + +In most other encodings, `\w` matches many more characters, including accented letters, Greek letters, +Cyrillic letters, Braille letters and numbers, Runic letters, Hebrew letters, Arabic letters and numerals, +Chinese Han ideographs, Japanese Katakana and Hiragana, Korean Hangul, and generally any symbol that +could qualify as a phonetic "letter" or counting "number" in any language. (Note that emoji are _not_ +considered "word characters.") + +`\W` always matches the opposite of whatever `\w` matches. + + +### 19. ONIG_SYN_OP_ESC_LTGT_WORD_BEGIN_END (enable `\<` and `\>`) + +_Set in: Grep, GnuRegex_ + +Enables support for the GNU-specific `\<` and `\>` word-boundary metacharacters. These work like +the `\b` word-boundary metacharacter, but only match at one end of the word or the other: `\<` +only matches at a transition from a non-word character to a word character (i.e., at the start +of a word), and `\>` only matches at a transition from a word character to a non-word character +(i.e., at the end of a word). + +Most regex syntaxes do _not_ support these metacharacters. + + +### 20. ONIG_SYN_OP_ESC_B_WORD_BOUND (enable `\b` and `\B`) + +_Set in: Grep, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the common `\b` and `\B` word-boundary metacharacters. The `\b` metacharacter +matches a zero-width position at a transition from word-characters to non-word-characters, or vice +versa. The `\B` metacharacter matches at all positions _not_ matched by `\b`. + +See details in `ONIG_SYN_OP_ESC_W_WORD` above for an explanation as to which characters +are considered "word characters." + + +### 21. ONIG_SYN_OP_ESC_S_WHITE_SPACE (enable `\s` and `\S`) + +_Set in: GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the common `\s` and `\S` whitespace-matching metacharacters. + +The `\s` metacharacter in ASCII encoding is exactly equivalent to the character class +`[\t\n\v\f\r ]`, or characters codes 9 through 13 (inclusive), and 32. + +The `\s` metacharacter in Unicode is exactly equivalent to the character class +`[\t\n\v\f\r \x85\xA0\x1680\x2000-\x200A\x2028-\x2029\x202F\x205F\x3000]` — that is, it matches +the same as ASCII, plus U+0085 (next line), U+00A0 (nonbreaking space), U+1680 (Ogham space mark), +U+2000 (en quad) through U+200A (hair space) (this range includes several widths of Unicode spaces), +U+2028 (line separator) through U+2029 (paragraph separator), +U+202F (narrow no-break space), U+205F (medium mathematical space), and U+3000 (CJK ideographic space). + +All non-Unicode encodings are handled by converting their code points to the appropriate +Unicode-equivalent code points, and then matching according to Unicode rules. + +`\S` always matches any one character that is _not_ in the set matched by `\s`. + + +### 22. ONIG_SYN_OP_ESC_D_DIGIT (enable `\d` and `\D`) + +_Set in: GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the common `\d` and `\D` digit-matching metacharacters. + +The `\d` metacharacter in ASCII encoding is exactly equivalent to the character class +`[0-9]`, or characters codes 48 through 57 (inclusive). + +The `\d` metacharacter in Unicode matches `[0-9]`, as well as digits in Arabic, Devanagari, +Bengali, Laotian, Mongolian, CJK fullwidth numerals, and many more. + +All non-Unicode encodings are handled by converting their code points to the appropriate +Unicode-equivalent code points, and then matching according to Unicode rules. + +`\D` always matches any one character that is _not_ in the set matched by `\d`. + + +### 23. ONIG_SYN_OP_LINE_ANCHOR (enable `^r` and `r$`) + +_Set in: Emacs, Grep, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the common `^` and `$` line-anchor metacharacters. + +In single-line mode, `^` matches the start of the input buffer, and `$` matches +the end of the input buffer. In multi-line mode, `^` matches if the preceding +character is `\n`; and `$` matches if the following character is `\n`. + +(Note that Oniguruma does not recognize other newline types: It only matches +`^` and `$` against `\n`: not `\r`, not `\r\n`, not the U+2028 line separator, +and not any other form.) + + +### 24. ONIG_SYN_OP_POSIX_BRACKET (enable POSIX `[:xxxx:]`) + +_Set in: PosixBasic, PosixExtended, Grep, GnuRegex, Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for the POSIX `[:xxxx:]` character classes, like `[:alpha:]` and `[:digit:]`. +The supported POSIX character classes are `alnum`, `alpha`, `blank`, `cntrl`, `digit`, +`graph`, `lower`, `print`, `punct`, `space`, `upper`, `xdigit`, `ascii`, `word`. + + +### 25. ONIG_SYN_OP_QMARK_NON_GREEDY (enable `r??`, `r*?`, `r+?`, and `r{n,m}?`) + +_Set in: Perl, Java, Perl_NG, Ruby, Oniguruma_ + +Enables support for lazy (non-greedy) quantifiers: That is, if you append a `?` after +another quantifier such as `?`, `*`, `+`, or `{n,m}`, Oniguruma will try to match +as _little_ as possible instead of as _much_ as possible. + + +### 26. ONIG_SYN_OP_ESC_CONTROL_CHARS (enable `\n`, `\r`, `\t`, etc.) + +_Set in: PosixBasic, PosixExtended, Java, Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for C-style control-code escapes, like `\n` and `\r`. Specifically, +this recognizes `\a` (7), `\b` (8), `\t` (9), `\n` (10), `\f` (12), `\r` (13), and +`\e` (27). If ONIG_SYN_OP2_ESC_V_VTAB is enabled (see below), this also enables +support for recognizing `\v` as code point 11. + + +### 27. ONIG_SYN_OP_ESC_C_CONTROL (enable `\cx` control codes) + +_Set in: Java, Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for named control-code escapes, like `\cm` or `\cM` for code-point +13. In this shorthand form, control codes may be specified by `\c` (for "Control") +followed by an alphabetic letter, a-z or A-Z, indicating which code point to represent +(1 through 26). So `\cA` is code point 1, and `\cZ` is code point 26. + + +### 28. ONIG_SYN_OP_ESC_OCTAL3 (enable `\OOO` octal codes) + +_Set in: Java, Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for octal-style escapes of up to three digits, like `\1` for code +point 1, and `\177` for code point 127. Octal values greater than 255 will result +in an error message. + + +### 29. ONIG_SYN_OP_ESC_X_HEX2 (enable `\xHH` hex codes) + +_Set in: Java, Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for hexadecimal-style escapes of up to two digits, like `\x1` for code +point 1, and `\x7F` for code point 127. + + +### 30. ONIG_SYN_OP_ESC_X_BRACE_HEX8 (enable `\x{7HHHHHHH}` hex codes) + +_Set in: Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for brace-wrapped hexadecimal-style escapes of up to eight digits, +like `\x{1}` for code point 1, and `\x{FFFE}` for code point 65534. + + +### 31. ONIG_SYN_OP_ESC_O_BRACE_OCTAL (enable `\o{1OOOOOOOOOO}` octal codes) + +_Set in: Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for brace-wrapped octal-style escapes of up to eleven digits, +like `\o{1}` for code point 1, and `\o{177776}` for code point 65534. + +(New feature as of Oniguruma 6.3.) + + +---------- + + +## Group Two Flags (op2) + + +This group contains support for lesser-known regex syntax constructs. + + +### 0. ONIG_SYN_OP2_ESC_CAPITAL_Q_QUOTE (enable `\Q...\E`) + +_Set in: Java, Perl, Perl_NG_ + +Enables support for "quoted" parts of a pattern: Between `\Q` and `\E`, all +syntax parsing is turned off, so that metacharacters like `*` and `+` will no +longer be treated as metacharacters, and instead will be matched as literal +`*` and `+`, as if they had been escaped with `\*` and `\+`. + + +### 1. ONIG_SYN_OP2_QMARK_GROUP_EFFECT (enable `(?...)`) + +_Set in: Java, Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for the fairly-common `(?...)` grouping operator, which +controls precedence but which does _not_ capture its contents. + + +### 2. ONIG_SYN_OP2_OPTION_PERL (enable options `(?imsx)` and `(?-imsx)`) + +_Set in: Java, Perl, Perl_NG_ + +Enables support of regex options. (i,m,s,x) +The supported toggle-able options for this flag are: + + - `i` - Case-insensitivity + - `m` - Multi-line mode (`^` and `$` match at `\n` as well as start/end of buffer) + - `s` - Single-line mode (`.` can match `\n`) + - `x` - Extended pattern (free-formatting: whitespace will ignored) + + +### 3. ONIG_SYN_OP2_OPTION_RUBY (enable options `(?imx)` and `(?-imx)`) + +_Set in: Ruby, Oniguruma_ + +Enables support of regex options. (i,m,x) +The supported toggle-able options for this flag are: + + - `i` - Case-insensitivity + - `m` - Multi-line mode (`.` can match `\n`) + - `x` - Extended pattern (free-formatting: whitespace will ignored) + + +### 4. ONIG_SYN_OP2_PLUS_POSSESSIVE_REPEAT (enable `r?+`, `r*+`, and `r++`) + +_Set in: Ruby, Oniguruma_ + +Enables support for the _possessive_ quantifiers `?+`, `*+`, and `++`, which +work similarly to `?` and `*` and `+`, respectively, but which do not backtrack +after matching: Like the normal greedy quantifiers, they match as much as +possible, but they do not attempt to match _less_ than their maximum possible +extent if subsequent parts of the pattern fail to match. + + +### 5. ONIG_SYN_OP2_PLUS_POSSESSIVE_INTERVAL (enable `r{n,m}+`) + +_Set in: Java_ + +Enables support for the _possessive_ quantifier `{n,m}+`, which +works similarly to `{n,m}`, but which does not backtrack +after matching: Like the normal greedy quantifier, it matches as much as +possible, but it do not attempt to match _less_ than its maximum possible +extent if subsequent parts of the pattern fail to match. + + +### 6. ONIG_SYN_OP2_CCLASS_SET_OP (enable `&&` within `[...]`) + +_Set in: Java, Ruby, Oniguruma_ + +Enables support for character-class _intersection_. For example, with this +feature enabled, you can write `[a-z&&[^aeiou]]` to produce a character class +of only consonants, or `[\0-\37&&[^\n\r]]` to produce a character class of +all control codes _except_ newlines. + + +### 7. ONIG_SYN_OP2_QMARK_LT_NAMED_GROUP (enable named captures `(?<name>...)`) + +_Set in: Perl_NG, Ruby, Oniguruma_ + +Enables support for _naming_ capture groups, so that instead of having to +refer to captures by position (like `\3` or `$3`), you can refer to them by names +(like `server` and `path`). This supports the Perl/Ruby naming syntaxes `(?<name>...)` +and `(?'name'...)`, but not the Python `(?P<name>...)` syntax. + + +### 8. ONIG_SYN_OP2_ESC_K_NAMED_BACKREF (enable named backreferences `\k<name>`) + +_Set in: Perl_NG, Ruby, Oniguruma_ + +Enables support for substituted backreferences by name, not just by position. +This supports using `\k'name'` in addition to supporting `\k<name>`. This also +supports an Oniguruma-specific extension that lets you specify the _distance_ of +the match, if the capture matched multiple times, by writing `\k<name+n>` or +`\k<name-n>`. + + +### 9. ONIG_SYN_OP2_ESC_G_SUBEXP_CALL (enable backreferences `\g<name>` and `\g<n>`) + +_Set in: Perl_NG, Ruby, Oniguruma_ + +Enables support for substituted backreferences by both name and position using +the same syntax. This supports using `\g'name'` and `\g'1'` in addition to +supporting `\g<name>` and `\g<1>`. + + +### 10. ONIG_SYN_OP2_ATMARK_CAPTURE_HISTORY (enable `(?@...)` and `(?@<name>...)`) + +_Set in: none_ + +Enables support for _capture history_, which can answer via the `onig_*capture*()` +functions exactly which captures were matched, how many times, and where in the +input they were matched, by placing `?@` in front of the capture. Per Oniguruma's +regex syntax documentation (appendix A-5): + +`/(?@a)*/.match("aaa")` ==> `[<0-1>, <1-2>, <2-3>]` + +This can require substantial memory, is primarily useful for debugging, and is not +enabled by default in any syntax. + + +### 11. ONIG_SYN_OP2_ESC_CAPITAL_C_BAR_CONTROL (enable `\C-x`) + +_Set in: Ruby, Oniguruma_ + +Enables support for Ruby legacy control-code escapes, like `\C-m` or `\C-M` for code-point +13. In this shorthand form, control codes may be specified by `\C-` (for "Control") +followed by a single character (or equivalent), indicating which code point to represent, +based on that character's lowest five bits. So, like `\c`, you can represent code-point +10 with `\C-j`, but you can also represent it with `\C-*` as well. + +See also ONIG_SYN_OP_ESC_C_CONTROL, which enables the more-common `\cx` syntax. + + +### 12. ONIG_SYN_OP2_ESC_CAPITAL_M_BAR_META (enable `\M-x`) + +_Set in: Ruby, Oniguruma_ + +Enables support for Ruby legacy meta-code escapes. When you write `\M-x`, Oniguruma +will match an `x` whose 8th bit is set (i.e., the character code of `x` will be or'ed +with `0x80`). So, for example, you can match `\x81` using `\x81`, or you can write +`\M-\1`. This is mostly useful when working with legacy 8-bit character encodings. + + +### 13. ONIG_SYN_OP2_ESC_V_VTAB (enable `\v` as vertical tab) + +_Set in: Java, Ruby, Oniguruma_ + +Enables support for a C-style `\v` escape code, meaning "vertical tab." If enabled, +`\v` will be equivalent to ASCII code point 11. + + +### 14. ONIG_SYN_OP2_ESC_U_HEX4 (enable `\uHHHH` for Unicode) + +_Set in: Java, Ruby, Oniguruma_ + +Enables support for a Java-style `\uHHHH` escape code for representing Unicode +code-points by number, using up to four hexadecimal digits (up to `\uFFFF`). So, +for example, `\u221E` will match an infinity symbol, `∞`. + +For code points larger than four digits, like the emoji `🚡` (aerial tramway, or code +point U+1F6A1), you must either represent the character directly using an encoding like +UTF-8, or you must enable support for ONIG_SYN_OP_ESC_X_BRACE_HEX8 or +ONIG_SYN_OP_ESC_O_BRACE_OCTAL, which support more than four digits. + +(New feature as of Oniguruma 6.7.) + + +### 15. ONIG_SYN_OP2_ESC_GNU_BUF_ANCHOR (enable ``\` `` and `\'` anchors) + +_Set in: Emacs_ + +This flag makes the ``\` `` and `\'` escapes function identically to +`\A` and `\z`, respectively (when ONIG_SYN_OP_ESC_AZ_BUF_ANCHOR is enabled). + +These anchor forms are very obscure, and rarely supported by other regex libraries. + + +### 16. ONIG_SYN_OP2_ESC_P_BRACE_CHAR_PROPERTY (enable `\p{...}` and `\P{...}`) + +_Set in: Java, Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for an alternate syntax for POSIX character classes; instead of +writing `[:alpha:]` when this is enabled, you can instead write `\p{alpha}`. + +See also ONIG_SYN_OP_POSIX_BRACKET for the classic POSIX form. + + +### 17. ONIG_SYN_OP2_ESC_P_BRACE_CIRCUMFLEX_NOT (enable `\p{^...}` and `\P{^...}`) + +_Set in: Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for an alternate syntax for POSIX character classes; instead of +writing `[:^alpha:]` when this is enabled, you can instead write `\p{^alpha}`. + +See also ONIG_SYN_OP_POSIX_BRACKET for the classic POSIX form. + + +### 18. ONIG_SYN_OP2_CHAR_PROPERTY_PREFIX_IS + +_(not presently used)_ + + +### 19. ONIG_SYN_OP2_ESC_H_XDIGIT (enable `\h` and `\H`) + +_Set in: Ruby, Oniguruma_ + +Enables support for the Ruby-specific shorthand `\h` and `\H` metacharacters. +Somewhat like `\d` matches decimal digits, `\h` matches hexadecimal digits — that is, +characters in `[0-9a-fA-F]`. + +`\H` matches the opposite of whatever `\h` matches. + + +### 20. ONIG_SYN_OP2_INEFFECTIVE_ESCAPE (disable `\`) + +_Set in: As-is_ + +If set, this disables all escape codes, shorthands, and metacharacters that start +with `\` (or whatever the configured escape character is), allowing `\` to be treated +as a literal `\`. + +You usually do not want this flag to be enabled. + + +### 21. ONIG_SYN_OP2_QMARK_LPAREN_IF_ELSE (enable `(?(...)then|else)`) + +_Set in: Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for conditional inclusion of subsequent regex patterns based on whether +a prior named or numbered capture matched, or based on whether a pattern will +match. This supports many different forms, including: + + - `(?(<foo>)then|else)` - condition based on a capture by name. + - `(?('foo')then|else)` - condition based on a capture by name. + - `(?(3)then|else)` - condition based on a capture by number. + - `(?(+3)then|else)` - forward conditional to a future match, by relative position. + - `(?(-3)then|else)` - backward conditional to a prior match, by relative position. + - `(?(foo)then|else)` - this matches a pattern `foo`. (foo is any sub-expression) + +(New feature as of Oniguruma 6.5.) + + +### 22. ONIG_SYN_OP2_ESC_CAPITAL_K_KEEP (enable `\K`) + +_Set in: Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for `\K`, which excludes all content before it from the overall +regex match (i.e., capture #0). So, for example, pattern `foo\Kbar` would match +`foobar`, but capture #0 would only include `bar`. + +(New feature as of Oniguruma 6.5.) + + +### 23. ONIG_SYN_OP2_ESC_CAPITAL_R_GENERAL_NEWLINE (enable `\R`) + +_Set in: Perl, Perl_NG, Ruby, Oniguruma_ + +Enables support for `\R`, the "general newline" shorthand, which matches +`(\r\n|[\n\v\f\r\u0085\u2028\u2029])` (obviously, the Unicode values are cannot be +matched in ASCII encodings). + +(New feature as of Oniguruma 6.5.) + + +### 24. ONIG_SYN_OP2_ESC_CAPITAL_N_O_SUPER_DOT (enable `\N` and `\O`) + +_Set in: Perl, Perl_NG, Oniguruma_ + +Enables support for `\N` and `\O`. `\N` is "not a line break," which is much +like the standard `.` metacharacter, except that while `.` can be affected by +the single-line setting, `\N` always matches exactly one character that is not +one of the various line-break characters (like `\n` and `\r`). + +`\O` matches exactly one character, regardless of whether single-line or +multi-line mode are enabled or disabled. + +(New feature as of Oniguruma 6.5.) + + +### 25. ONIG_SYN_OP2_QMARK_TILDE_ABSENT_GROUP (enable `(?~...)`) + +_Set in: Ruby, Oniguruma_ + +Enables support for the `(?~r)` "absent operator" syntax, which matches +as much as possible as long as the result _doesn't_ match pattern `r`. This is +_not_ the same as negative lookahead or negative lookbehind. + +Among the most useful examples of this is `\/\*(?~\*\/)\*\/`, which matches +C-style comments by simply saying "starts with /*, ends with */, and _doesn't_ +contain a */ in between." + +A full explanation of this feature is complicated, but it is useful, and an +excellent article about it is [available on Medium](https://medium.com/rubyinside/the-new-absent-operator-in-ruby-s-regular-expressions-7c3ef6cd0b99). + +(New feature as of Oniguruma 6.5.) + + +### 26. ONIG_SYN_OP2_ESC_X_Y_TEXT_SEGMENT (enable `\X` and `\Y` and `\y`) + +_Set in: Perl, Perl_NG, Ruby, Oniguruma_ + +`\X` is another variation on `.`, designed to support Unicode, in that it matches +a full _grapheme cluster_. In Unicode, `à` can be encoded as one code point, +`U+00E0`, or as two, `U+0061 U+0300`. If those are further escaped using UTF-8, +the former becomes two bytes, and the latter becomes three. Unfortunately, `.` +would naively match only one or two bytes, depending on the encoding, and would +likely incorrectly match anything from just `a` to a broken half of a code point. +`\X` is designed to fix this: It matches the full `à`, no matter how `à` is +encoded or decomposed. + +`\y` matches a cluster boundary, i.e., a zero-width position between +graphemes, somewhat like `\b` matches boundaries between words. `\Y` matches +the _opposite_ of `\y`, that is, a zero-width position between code points in +the _middle_ of a grapheme. + +(New feature as of Oniguruma 6.6.) + + +### 27. ONIG_SYN_OP2_QMARK_PERL_SUBEXP_CALL (enable `(?R)` and `(?&name)`) + +_Set in: Perl_NG_ + +Enables support for substituted backreferences by both name and position using +Perl-5-specific syntax. This supports using `(?R3)` and `(?&name)` to reference +previous (and future) matches, similar to the more-common `\g<3>` and `\g<name>` +backreferences. + +(New feature as of Oniguruma 6.7.) + + +### 28. ONIG_SYN_OP2_QMARK_BRACE_CALLOUT_CONTENTS (enable `(?{...})`) + +_Set in: Perl, Perl_NG, Oniguruma_ + +Enables support for Perl-style "callouts" — pattern substitutions that result from +invoking a callback method. When `(?{foo})` is reached in a pattern, the callback +function set in `onig_set_progress_callout()` will be invoked, and be able to perform +custom computation during the pattern match (and during backtracking). + +Full documentation for this advanced feature can be found in the Oniguruma +`docs/CALLOUT.md` file, with an example in `samples/callout.c`. + +(New feature as of Oniguruma 6.8.) + + +### 29. ONIG_SYN_OP2_ASTERISK_CALLOUT_NAME (enable `(*name)`) + +_Set in: Perl, Perl_NG, Oniguruma_ + +Enables support for Perl-style "callouts" — pattern substitutions that result from +invoking a callback method. When `(*foo)` is reached in a pattern, the callback +function set in `onig_set_callout_of_name()` will be invoked, passing the given name +`foo` to it, and it can perform custom computation during the pattern match (and +during backtracking). + +Full documentation for this advanced feature can be found in the Oniguruma +`docs/CALLOUT.md` file, with an example in `samples/callout.c`. + +(New feature as of Oniguruma 6.8.) + + +### 30. ONIG_SYN_OP2_OPTION_ONIGURUMA (enable options `(?imxWSDPy)` and `(?-imxWDSP)`) + +_Set in: Oniguruma_ + +Enables support of regex options. (i,m,x,W,S,D,P,y) + +(New feature as of Oniguruma 6.9.2) + + - `i` - Case-insensitivity + - `m` - Multi-line mode (`.` can match `\n`) + - `x` - Extended pattern (free-formatting: whitespace will ignored) + - `W` - ASCII only word. + - `D` - ASCII only digit. + - `S` - ASCII only space. + - `P` - ASCII only POSIX properties. (includes W,D,S) + +---------- + + +## Syntax Flags (syn) + + +This group contains rules to handle corner cases and constructs that are errors in +some syntaxes but not in others. + +### 0. ONIG_SYN_CONTEXT_INDEP_REPEAT_OPS (independent `?`, `*`, `+`, `{n,m}`) + +_Set in: PosixExtended, GnuRegex, Java, Perl, Perl_NG, Ruby, Oniguruma_ + +This flag specifies how to handle operators like `?` and `*` when they aren't +directly attached to an operand, as in `^*` or `(*)`: Are they an error, are +they discarded, or are they taken as literals? If this flag is clear, they +are taken as literals; otherwise, the ONIG_SYN_CONTEXT_INVALID_REPEAT_OPS flag +determines if they are errors or if they are discarded. + +### 1. ONIG_SYN_CONTEXT_INVALID_REPEAT_OPS (error or ignore independent operators) + +_Set in: PosixExtended, GnuRegex, Java, Perl, Perl_NG, Ruby, Oniguruma_ + +If ONIG_SYN_CONTEXT_INDEP_REPEAT_OPS is set, this flag controls what happens when +independent operators appear in a pattern: If this flag is set, then independent +operators produce an error message; if this flag is clear, then independent +operators are silently discarded. + +### 2. ONIG_SYN_ALLOW_UNMATCHED_CLOSE_SUBEXP (allow `...)...`) + +_Set in: PosixExtended_ + +This flag, if set, causes a `)` character without a preceding `(` to be treated as +a literal `)`, equivalent to `\)`. If this flag is clear, then an unmatched `)` +character will produce an error message. + +### 3. ONIG_SYN_ALLOW_INVALID_INTERVAL (allow `{???`) + +_Set in: GnuRegex, Java, Perl, Perl_NG, Ruby, Oniguruma_ + +This flag, if set, causes an invalid range, like `foo{bar}` or `foo{}`, to be +silently discarded, as if `foo` had been written instead. If clear, an invalid +range will produce an error message. + +### 4. ONIG_SYN_ALLOW_INTERVAL_LOW_ABBREV (allow `{,n}` to mean `{0,n}`) + +_Set in: Ruby, Oniguruma_ + +If this flag is set, then `r{,n}` will be treated as equivalent to writing +`{0,n}`. If this flag is clear, then `r{,n}` will produce an error message. + +Note that regardless of whether this flag is set or clear, if +ONIG_SYN_OP_BRACE_INTERVAL is enabled, then `r{n,}` will always be legal: This +flag *only* controls the behavior of the opposite form, `r{,n}`. + +### 5. ONIG_SYN_STRICT_CHECK_BACKREF (error on invalid backrefs) + +_Set in: none_ + +If this flag is set, an invalid backref, like `\1` in a pattern with no captures, +will produce an error. If this flag is clear, then an invalid backref will be +equivalent to the empty string. + +No built-in syntax has this flag enabled. + +### 6. ONIG_SYN_DIFFERENT_LEN_ALT_LOOK_BEHIND (allow `(?<=a|bc)`) + +_Set in: Java, Ruby, Oniguruma_ + +If this flag is set, lookbehind patterns with alternate options may have differing +lengths among those options. If this flag is clear, lookbehind patterns with options +must have each option have identical length to the other options. + +Oniguruma can handle either form, but not all regex engines can, so for compatibility, +Oniguruma allows you to cause regexes for other regex engines to fail if they might +depend on this rule. + +### 7. ONIG_SYN_CAPTURE_ONLY_NAMED_GROUP (prefer `\k<name>` over `\3`) + +_Set in: Perl_NG, Ruby, Oniguruma_ + +If this flag is set on the syntax *and* ONIG_OPTION_CAPTURE_GROUP is set when calling +Oniguruma, then if a name is used on any capture, all captures must also use names: A +single use of a named capture prohibits the use of numbered captures. + +### 8. ONIG_SYN_ALLOW_MULTIPLEX_DEFINITION_NAME (allow `(?<x>)...(?<x>)`) + +_Set in: Perl_NG, Ruby, Oniguruma_ + +If this flag is set, multiple capture groups may use the same name. If this flag is +clear, then reuse of a name will produce an error message. + +### 9. ONIG_SYN_FIXED_INTERVAL_IS_GREEDY_ONLY (`a{n}?` is equivalent to `(?:a{n})?`) + +_Set in: Ruby, Oniguruma_ + +If this flag is set, then intervals of a fixed size will ignore a lazy (non-greedy) +`?` quantifier and treat it as an optional match (an ordinary `r?`), since "match as +little as possible" is meaningless for a fixed-size interval. If this flag is clear, +then `r{n}?` will mean the same as `r{n}`, and the useless `?` will be discarded. + +### 20. ONIG_SYN_NOT_NEWLINE_IN_NEGATIVE_CC (add `\n` to `[^...]`) + +_Set in: Grep_ + +If this flag is set, all newline characters (like `\n`) will be excluded from a negative +character class automatically, as if the pattern had been written as `[^...\n]`. If this +flag is clear, negative character classes do not automatically exclude newlines, and +only exclude those characters and ranges written in them. + +### 21. ONIG_SYN_BACKSLASH_ESCAPE_IN_CC (allow `[...\w...]`) + +_Set in: GnuRegex, Java, Perl, Perl_NG, Ruby, Oniguruma_ + +If this flag is set, shorthands like `\w` are allowed to describe characters in character +classes. If this flag is clear, shorthands like `\w` are treated as a redundantly-escaped +literal `w`. + +### 22. ONIG_SYN_ALLOW_EMPTY_RANGE_IN_CC (silently discard `[z-a]`) + +_Set in: Emacs, Grep_ + +If this flag is set, then character ranges like `[z-a]` that are broken or contain no +characters will be silently ignored. If this flag is clear, then broken or empty +character ranges will produce an error message. + +### 23. ONIG_SYN_ALLOW_DOUBLE_RANGE_OP_IN_CC (treat `[0-9-a]` as `[0-9\-a]`) + +_Set in: PosixExtended, GnuRegex, Java, Perl, Perl_NG, Ruby, Oniguruma_ + +If this flag is set, then a trailing `-` after a character range will be taken as a +literal `-`, as if it had been escaped as `\-`. If this flag is clear, then a trailing +`-` after a character range will produce an error message. + +### 24. ONIG_SYN_WARN_CC_OP_NOT_ESCAPED (warn on `[[...]` and `[-x]`) + +_Set in: Ruby, Oniguruma_ + +If this flag is set, Oniguruma will be stricter about warning for bad forms in +character classes: `[[...]` will produce a warning, but `[\[...]` will not; +`[-x]` will produce a warning, but `[\-x]` will not; `[x&&-y]` will produce a warning, +while `[x&&\-y]` will not; and so on. If this flag is clear, all of these warnings +will be silently discarded. + +### 25. ONIG_SYN_WARN_REDUNDANT_NESTED_REPEAT (warn on `(?:a*)+`) + +_Set in: Ruby, Oniguruma_ + +If this flag is set, Oniguruma will warn about nested repeat operators those have no meaning, like `(?:a*)+`. +If this flag is clear, Oniguruma will allow the nested repeat operators without warning about them. + +### 31. ONIG_SYN_CONTEXT_INDEP_ANCHORS + +_Set in: PosixExtended, GnuRegex, Java, Perl, Perl_NG, Ruby, Oniguruma_ + +Not currently used, and does nothing. (But still set in several syntaxes for some +reason.) + +---------- + +## Usage tables + +These tables show which of the built-in syntaxes use which flags and options, for easy comparison between them. + +### Group One Flags (op) + +| ID | Option | PosB | PosEx | Emacs | Grep | Gnu | Java | Perl | PeNG | Ruby | Onig | +| ----- | --------------------------------------------- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | +| 0 | `ONIG_SYN_OP_VARIABLE_META_CHARACTERS` | - | - | - | - | - | - | - | - | - | - | +| 1 | `ONIG_SYN_OP_DOT_ANYCHAR` | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | +| 2 | `ONIG_SYN_OP_ASTERISK_ZERO_INF` | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | +| 3 | `ONIG_SYN_OP_ESC_ASTERISK_ZERO_INF` | - | - | - | - | - | - | - | - | - | - | +| 4 | `ONIG_SYN_OP_PLUS_ONE_INF` | - | Yes | Yes | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 5 | `ONIG_SYN_OP_ESC_PLUS_ONE_INF` | - | - | - | Yes | - | - | - | - | - | - | +| 6 | `ONIG_SYN_OP_QMARK_ZERO_ONE` | - | Yes | Yes | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 7 | `ONIG_SYN_OP_ESC_QMARK_ZERO_ONE` | - | - | - | Yes | - | - | - | - | - | - | +| 8 | `ONIG_SYN_OP_BRACE_INTERVAL` | - | Yes | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 9 | `ONIG_SYN_OP_ESC_BRACE_INTERVAL` | Yes | - | Yes | Yes | - | - | - | - | - | - | +| 10 | `ONIG_SYN_OP_VBAR_ALT` | - | Yes | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 11 | `ONIG_SYN_OP_ESC_VBAR_ALT` | - | - | Yes | Yes | - | - | - | - | - | - | +| 12 | `ONIG_SYN_OP_LPAREN_SUBEXP` | - | Yes | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 13 | `ONIG_SYN_OP_ESC_LPAREN_SUBEXP` | Yes | - | Yes | Yes | - | - | - | - | - | - | +| 14 | `ONIG_SYN_OP_ESC_AZ_BUF_ANCHOR` | - | - | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 15 | `ONIG_SYN_OP_ESC_CAPITAL_G_BEGIN_ANCHOR` | - | - | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 16 | `ONIG_SYN_OP_DECIMAL_BACKREF` | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | +| 17 | `ONIG_SYN_OP_BRACKET_CC` | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | +| 18 | `ONIG_SYN_OP_ESC_W_WORD` | - | - | - | Yes | Yes | Yes | Yes | Yes | Yes | Yes | +| 19 | `ONIG_SYN_OP_ESC_LTGT_WORD_BEGIN_END` | - | - | - | Yes | Yes | - | - | - | - | - | +| 20 | `ONIG_SYN_OP_ESC_B_WORD_BOUND` | - | - | - | Yes | Yes | Yes | Yes | Yes | Yes | Yes | +| 21 | `ONIG_SYN_OP_ESC_S_WHITE_SPACE` | - | - | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 22 | `ONIG_SYN_OP_ESC_D_DIGIT` | - | - | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 23 | `ONIG_SYN_OP_LINE_ANCHOR` | - | - | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | +| 24 | `ONIG_SYN_OP_POSIX_BRACKET` | Yes | Yes | Yes | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 25 | `ONIG_SYN_OP_QMARK_NON_GREEDY` | - | - | - | - | - | Yes | Yes | Yes | Yes | Yes | +| 26 | `ONIG_SYN_OP_ESC_CONTROL_CHARS` | Yes | Yes | - | - | - | Yes | Yes | Yes | Yes | Yes | +| 27 | `ONIG_SYN_OP_ESC_C_CONTROL` | - | - | - | - | - | Yes | Yes | Yes | Yes | Yes | +| 28 | `ONIG_SYN_OP_ESC_OCTAL3` | - | - | - | - | - | Yes | Yes | Yes | Yes | Yes | +| 29 | `ONIG_SYN_OP_ESC_X_HEX2` | - | - | - | - | - | Yes | Yes | Yes | Yes | Yes | +| 30 | `ONIG_SYN_OP_ESC_X_BRACE_HEX8` | - | - | - | - | - | - | Yes | Yes | Yes | Yes | +| 31 | `ONIG_SYN_OP_ESC_O_BRACE_OCTAL` | - | - | - | - | - | - | Yes | Yes | Yes | Yes | + +### Group Two Flags (op2) + +| ID | Option | PosB | PosEx | Emacs | Grep | Gnu | Java | Perl | PeNG | Ruby | Onig | +| ----- | --------------------------------------------- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | +| 0 | `ONIG_SYN_OP2_ESC_CAPITAL_Q_QUOTE` | - | - | - | - | - | Yes | Yes | Yes | - | - | +| 1 | `ONIG_SYN_OP2_QMARK_GROUP_EFFECT` | - | - | - | - | - | Yes | Yes | Yes | Yes | Yes | +| 2 | `ONIG_SYN_OP2_OPTION_PERL` | - | - | - | - | - | Yes | Yes | Yes | - | - | +| 3 | `ONIG_SYN_OP2_OPTION_RUBY` | - | - | - | - | - | - | - | - | Yes | - | +| 4 | `ONIG_SYN_OP2_PLUS_POSSESSIVE_REPEAT` | - | - | - | - | - | - | - | - | Yes | Yes | +| 5 | `ONIG_SYN_OP2_PLUS_POSSESSIVE_INTERVAL` | - | - | - | - | - | Yes | - | - | - | - | +| 6 | `ONIG_SYN_OP2_CCLASS_SET_OP` | - | - | - | - | - | - | - | Yes | Yes | Yes | +| 7 | `ONIG_SYN_OP2_QMARK_LT_NAMED_GROUP` | - | - | - | - | - | - | - | Yes | Yes | Yes | +| 8 | `ONIG_SYN_OP2_ESC_K_NAMED_BACKREF` | - | - | - | - | - | - | - | Yes | Yes | Yes | +| 9 | `ONIG_SYN_OP2_ESC_G_SUBEXP_CALL` | - | - | - | - | - | - | - | Yes | Yes | Yes | +| 10 | `ONIG_SYN_OP2_ATMARK_CAPTURE_HISTORY` | - | - | - | - | - | - | - | - | - | - | +| 11 | `ONIG_SYN_OP2_ESC_CAPITAL_C_BAR_CONTROL` | - | - | - | - | - | - | - | - | Yes | Yes | +| 12 | `ONIG_SYN_OP2_ESC_CAPITAL_M_BAR_META` | - | - | - | - | - | - | - | - | Yes | Yes | +| 13 | `ONIG_SYN_OP2_ESC_V_VTAB` | - | - | - | - | - | Yes | - | - | Yes | Yes | +| 14 | `ONIG_SYN_OP2_ESC_U_HEX4` | - | - | - | - | - | Yes | - | - | Yes | Yes | +| 15 | `ONIG_SYN_OP2_ESC_GNU_BUF_ANCHOR` | - | - | Yes | - | - | - | - | - | - | - | +| 16 | `ONIG_SYN_OP2_ESC_P_BRACE_CHAR_PROPERTY` | - | - | - | - | - | Yes | Yes | Yes | Yes | Yes | +| 17 | `ONIG_SYN_OP2_ESC_P_BRACE_CIRCUMFLEX_NOT` | - | - | - | - | - | - | Yes | Yes | Yes | Yes | +| 18 | `ONIG_SYN_OP2_CHAR_PROPERTY_PREFIX_IS` | - | - | - | - | - | - | - | - | - | - | +| 19 | `ONIG_SYN_OP2_ESC_H_XDIGIT` | - | - | - | - | - | - | - | - | Yes | Yes | +| 20 | `ONIG_SYN_OP2_INEFFECTIVE_ESCAPE` | - | - | - | - | - | - | - | - | - | - | +| 21 | `ONIG_SYN_OP2_QMARK_LPAREN_IF_ELSE` | - | - | - | - | - | - | Yes | Yes | Yes | Yes | +| 22 | `ONIG_SYN_OP2_ESC_CAPITAL_K_KEEP` | - | - | - | - | - | - | Yes | Yes | Yes | Yes | +| 23 | `ONIG_SYN_OP2_ESC_CAPITAL_R_GENERAL_NEWLINE` | - | - | - | - | - | - | Yes | Yes | Yes | Yes | +| 24 | `ONIG_SYN_OP2_ESC_CAPITAL_N_O_SUPER_DOT` | - | - | - | - | - | - | Yes | Yes | - | Yes | +| 25 | `ONIG_SYN_OP2_QMARK_TILDE_ABSENT_GROUP` | - | - | - | - | - | - | - | - | Yes | Yes | +| 26 | `ONIG_SYN_OP2_ESC_X_Y_TEXT_SEGMENT` | - | - | - | - | - | - | Yes | Yes | Yes | Yes | +| 27 | `ONIG_SYN_OP2_QMARK_PERL_SUBEXP_CALL` | - | - | - | - | - | - | - | Yes | - | - | +| 28 | `ONIG_SYN_OP2_QMARK_BRACE_CALLOUT_CONTENTS` | - | - | - | - | - | - | Yes | Yes | Yes | - | +| 29 | `ONIG_SYN_OP2_ASTERISK_CALLOUT_NAME` | - | - | - | - | - | - | Yes | Yes | Yes | - | +| 30 | `ONIG_SYN_OP2_OPTION_ONIGURUMA` | - | - | - | - | - | - | - | - | - | Yes | + +### Syntax Flags (syn) + +| ID | Option | PosB | PosEx | Emacs | Grep | Gnu | Java | Perl | PeNG | Ruby | Onig | +| ----- | --------------------------------------------- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | ----- | +| 0 | `ONIG_SYN_CONTEXT_INDEP_REPEAT_OPS` | - | Yes | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 1 | `ONIG_SYN_CONTEXT_INVALID_REPEAT_OPS` | - | - | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 2 | `ONIG_SYN_ALLOW_UNMATCHED_CLOSE_SUBEXP` | - | Yes | - | - | - | - | - | - | - | - | +| 3 | `ONIG_SYN_ALLOW_INVALID_INTERVAL` | - | - | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 4 | `ONIG_SYN_ALLOW_INTERVAL_LOW_ABBREV` | - | - | - | - | - | - | - | - | Yes | Yes | +| 5 | `ONIG_SYN_STRICT_CHECK_BACKREF` | - | - | - | - | - | - | - | - | - | - | +| 6 | `ONIG_SYN_DIFFERENT_LEN_ALT_LOOK_BEHIND` | - | - | - | - | - | - | - | Yes | Yes | Yes | +| 7 | `ONIG_SYN_CAPTURE_ONLY_NAMED_GROUP` | - | - | - | - | - | - | - | Yes | Yes | Yes | +| 8 | `ONIG_SYN_ALLOW_MULTIPLEX_DEFINITION_NAME` | - | - | - | - | - | - | - | Yes | Yes | Yes | +| 9 | `ONIG_SYN_FIXED_INTERVAL_IS_GREEDY_ONLY` | - | - | - | - | - | - | - | - | Yes | Yes | +| 20 | `ONIG_SYN_NOT_NEWLINE_IN_NEGATIVE_CC` | - | - | - | Yes | - | - | - | - | - | - | +| 21 | `ONIG_SYN_BACKSLASH_ESCAPE_IN_CC` | - | - | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 22 | `ONIG_SYN_ALLOW_EMPTY_RANGE_IN_CC` | - | - | Yes | Yes | - | - | - | - | - | - | +| 23 | `ONIG_SYN_ALLOW_DOUBLE_RANGE_OP_IN_CC` | - | Yes | - | - | Yes | Yes | Yes | Yes | Yes | Yes | +| 24 | `ONIG_SYN_WARN_CC_OP_NOT_ESCAPED` | - | - | - | - | - | - | - | - | Yes | Yes | +| 25 | `ONIG_SYN_WARN_REDUNDANT_NESTED_REPEAT` | - | - | - | - | - | - | - | - | Yes | Yes | +| 31 | `ONIG_SYN_CONTEXT_INDEP_ANCHORS` | - | Yes | - | - | Yes | Yes | Yes | Yes | Yes | Yes | |