anchor.diff:        character, or at the subject begin (except if specified that the
         subject begin is not a start of line).
   * `$` matches at the end of a line, that is just before a new line, or
  -      at the subject end (except if specified that the subject end
  +      at the subject end (except if specified that the subject's end
         is not an end of line).
   * `\b` matches at a word boundary, when one of the previous character
          and current character is a word character, and the other is not.
  
positive.code: Modifiers
  ---------
  
  Some modifiers can control the matching behaviour of the atoms following
  them:
  
  * `(?i)` will enable case insensitive matching.
  * `(?I)` will disable case insensitive matching.
  
  Quoting
  -------
  
negative.code: * `\n` matches the line feed character.
  * `\r` matches the carriage return character.
  * `\t` matches the tabulation character.
  * `\v` matches the vertical tabulation character.
  
  Character classes
  -----------------
  