     newline (\x0a)
  \qdd       set the PCRE_MATCH_LIMIT limit to dd (any number of digits)
  \r         carriage return (\x0d)
  \t         tab (\x09)
  \v         vertical tab (\x0b)
  \nnn       octal character (up to 3 octal digits)
  \xhh       hexadecimal character (up to 2 hex digits)
  \x{hh...}  hexadecimal character, any number of digits in UTF-8 mode
  \A         pass the PCRE_ANCHORED option to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>
  \B         pass the PCRE_NOTBOL option to <b>pcre_exec