grammar JavascriptRegexp
  root <- ( ( "/" regexp "/" _flags:[igm]* ) / regexp ""? ) <Root>
  regexp <- _match:match _alternates:( "|" match )* <Regexp>
  match <- _anchor_start:anchor_start?
           (!repeat) _parts:match_fragment*
           _anchor_end:anchor_end? <Match>
  match_fragment <- _content:( subexp / charset / terminal ) _repeat:repeat? <MatchFragment>
  anchor_start <- "^"
  anchor_end <- "$"
  repeat <- _spec:( repeat_any / repeat_required / repeat_optional / repeat_spec ) _greedy:repeat_greedy? <Repeat>
  repeat_any <- "*" <RepeatAny>
  repeat_required <- "+" <RepeatRequired>
  repeat_optional <- "?" <RepeatOptional>
  repeat_spec <- ( "{" _min:[0-9]+ "," _max:[0-9]+ "}"
                 / "{," _max:[0-9]+ "}"
                 / "{" _min:[0-9]+ ",}"
                 / "{" _exact:[0-9]+ "}" ) <RepeatSpec>
  repeat_greedy <- "?"
  subexp <- "(" ( subexp_no_capture / subexp_positive_lookahead / subexp_negative_lookahead )? regexp ")" <Subexp>
  subexp_no_capture <- "?:"
  subexp_positive_lookahead <- "?="
  subexp_negative_lookahead <- "?!"
  charset <- "[" "^"? ( charset_range / charset_terminal )* "]" <Charset>
  charset_range <- charset_terminal "-" charset_terminal
  charset_terminal <- charset_escape / charset_literal
  charset_escape <- ( backspace_esc
                    / control_esc
                    / digit_esc
                    / non_digit_esc
                    / form_feed_esc
                    / line_feed_esc
                    / carriage_return_esc
                    / white_space_esc
                    / non_white_space_esc
                    / tab_esc
                    / vertical_tab_esc
                    / word_esc
                    / non_word_esc
                    / octal_esc
                    / hex_esc
                    / unicode_esc
                    / null_esc
                    / literal_esc )
  charset_literal <- [^\\\]]
  terminal <- any_character / escape / literal <Terminal>
  any_character <- "."
  escape <- ( word_boundary_esc
            / non_word_boundary_esc
            / control_esc
            / digit_esc
            / non_digit_esc
            / form_feed_esc
            / line_feed_esc
            / carriage_return_esc
            / white_space_esc
            / non_white_space_esc
            / tab_esc
            / vertical_tab_esc
            / word_esc
            / non_word_esc
            / back_reference
            / octal_esc
            / hex_esc
            / unicode_esc
            / null_esc
            / literal_esc )
  literal <- [^|\\/.\[\(\)?+*$^]
  back_reference <- "\\" [1-9]
  word_boundary_esc <- "\\b"
  non_word_boundary_esc <- "\\B"
  backspace_esc <- "\\b"
  control_esc <- "\\b" .
  digit_esc <- "\\d"
  non_digit_esc <- "\\D"
  form_feed_esc <- "\\f"
  line_feed_esc <- "\\n"
  carriage_return_esc <- "\\r"
  white_space_esc <- "\\s"
  non_white_space_esc <- "\\S"
  tab_esc <- "\\t"
  vertical_tab_esc <- "\\v"
  word_esc <- "\\w"
  non_word_esc <- "\\W"
  octal_esc <- "\\0" [0-7]+
  hex_esc <- "\\x" [0-9a-fA-F] [0-9a-fA-F]
  unicode_esc <- "\\u" [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F]
  null_esc <- "\\0"
  literal_esc <- "\\" .