public String getPrefix() {
      CharSequence chars = document.getCharsSequence();
      int end = start;
      for (int i = start - 1; i > lineStart; i--) {
        char c = chars.charAt(i);
        if (c == ':' || Character.isWhitespace(c)) {
          end--;
        }
        else {
          break;
        }
      }
      return CharMatcher.whitespace().trimFrom(chars.subSequence(lineStart, end));
    }
public String getPrefix()