regex_flavour.md

Syntax

1. Syntax Elements

   • \ Escape (Enables or disables metachar)
   • | Alternation
   • (...) Group
   • [...] Character Class
   • {{...}} Rule embed
   • \E{...} Embedded Code

2. Characters

   • \t Horizontal Tab (0x09)
   • \v Vertical Tab (0x0b)
   • \n Newline (LF) (0x0a)
   • \r Carriage Return (0x0d)
   • \b Backspace (0x08)
   • \f Form Feed (0x0c)
   • \a Bell (0x07)
   • \uHHHHHHHH Wide Unicode codepoint (Code point value)

3. Character Types

   1. Classes

      • . Any character except newline
      • \w Word character (Letter|Mark|Number|Connector Punc)
      • \W non-word character (reverse of \w)
      • \s Whitespace character (Line Sep | Par Sep | Space Sep)
      • \S non-whitespace character (reverse of \s)
      • \d Decimal digit character (Number Decimal)
      • \D non-digit character (reverse of \d)

   2. Unicode Classes or properties

      • \p{property-name} Unicode Class (L|Z|M|N|P) and their subcategories

4. Quantifiers

   1. Greedy

      • ? 1 or 0 times
      • * 0 or more times
      • + 1 or more times
      • {n,m} (n <= m) at least n but no more than m times
      • {n,} at least n times
      • {n} n times

   2. Reluctant

      • *? 0 or more times
      • +? 1 or more times

5. Assertions

   • ^ beginning of line
   • $ end of line
   • \b word boundary
   • \B non-word boundary
   • \A True beginning of string
   • \G beginning of match
   • \K set reported start of match

6. Character Classes (Note: Alternation of character classes merges them together)

   • ^... negative character class

7. Extended Groups (not yet implemented)

   • (?:...) Shy group (non-capturing)
   • (?imIM:subexp) specify option for match of subexp (not a group)
     • i: ignore case
     • m: multiline
     • I: match case
     • M: non multiline

8. Backreferences (not yet implemented)

   • Explanation: Backreferencing a group means to re-match its actual matched value
   • \<n> backreference group number n

9. Subexpr calls (in testing)

   • Explanation: Subexpr calling attempts to match a given group again, and then continuing from the ending position (if the match was a success) or terminating and reverting to the closest valid match
   • \g<n> attempt to call the nth group (leftmost calls are undefined)

10. Capture groups (indexing only)

    • (...) is a capture group and its index is the number of open-parens since the beginning of the regexp (unique)
    • (?|...) branch reset group: all alternative captures inside this group will start with the same group index
    • (?#...) inline comment: text inside this 'group' is ignored by the engine (the starting paren still increments the next capture index)

11. Embedded Rule Actions (WIP)

    • Appears as an escaped entity \E{...}, and acts on its own
    • Is run after the subexpression before it is successfully matched
    • Toplevel syntax:
      • \E{ statement-list } where
        • statement-list : expression ';' statement-list |
        • expression : ifexpr | loopexpr | wloopexpr | callexpr | number | opexpr
        • ifexpr : 'if' expression 'then' expression 'else' expression
        • loopexpr : 'for' identifier '=' expression ',' expression (',' expression)? 'in' expression
        • wloopexpr : 'while' expression 'in' expression
        • callexpr : identifier '(' arglist ')'
        • arglist : expression (',' arglist)? |
        • opexpr : operator expression | expression operator expression
        • operator : <defined single character>

Basic Features

support	'+' quantifier	Nested character classes	Non-greedy quantifiers	Non-capturing groups	Recursion	Lookahead	Lookbehind	Backreferences	Indexable captures	Directives	Conditionals	Atomic Groups	Named Captures	Comments	Embedded code	Unicode Property	Balancing Groups	Variable length lookbehind
Current support	Yes	No	Yes	Yes	WIP	No	No	No	Yes	No	No	Yes	No	Yes	Yes	Partial	No	No
Planned support	-	No	-	-	Yes	Yes	Yes	Yes	-	Yes	No	-	No	Yes	WIP	Yes	No	No

API features

support	UTF-16	UTF-8	Multiline	Partial match
Current	No	Yes	Yes	Only if partial rule exists
Planned	No	-	-	-