abstract class Pattern {
 /**
  * Match this pattern against the string repeatedly.
  *
  * The iterable will contain all the non-overlapping matches of the
  * pattern on the string, ordered by start index.
  *
  * The matches are found by repeatedly finding the first match
  * of the pattern on the string, starting from the end of the previous
  * match, and initially starting from index zero.
  *
  * If the pattern matches the empty string at some point, the next
  * match is found by starting at the previous match's end plus one.
  */
 Iterable<Match> allMatches(String str);

 /**
  * Match this pattern against the start of string.
  *
  * If [start] is provided, it must be an integer in the range `0` ..
  * `string.length`. In that case, this patten is tested against the
  * string at the [start] position. That is, a match is returned if the
  * pattern can match a part of the string starting from position [start].
  */
 Match matchAsPrefix(String string, [int start = 0]);
}