anchor.diff:  /**
    * Abstract character matcher.
    *
  - * The [CharMatcher] a boolean predicate on characters. The inclusion of a
  + * The [CharMatcher] is a boolean predicate on characters. The inclusion of a
    * character can be determined by calling the matcher with the code-unit
  - * of a character as a function argument, for example:
  + * of a character as the function argument, for example:
    *
    *     WHITESPACE(' '.codeUnitAt(0)); // true
    *     DIGIT('a'.codeUnitAt(0)); // false
  
positive.code:   }
  
    /**
     * Returns the last matching index in [sequence] starting at [start]
     * (inclusive). Returns -1 if it could not be found.
     */
    int lastIndexIn(String sequence, [int start]) {
      var codeUnits = sequence.codeUnits;
  
negative.code:   }
  
    /**
     * Returns the last matching index in [sequence] starting at [start]
     * (inclusive). Returns -1 if it could not be found.
     */
    int firstIndexIn(String sequence, [int start = 0]) {
      var codeUnits = sequence.codeUnits;
  