code: @Override
      public int start(String name) {
          Integer id = re.groupId(name);
          if (id == null) throw new IllegalArgumentException("<" + name + "> isn't defined");
          return start(id);
      }
docs: Returns the start index of the subsequence captured by the given
  named-capturing group during the previous match operation.
  
  @param name The name of a named capturing group in this matcher's pattern
  @return The index of the first character captured by the group,
  or <tt>-1</tt> if the match was successful but the group
  itself did not match anything