code: public final boolean skipDoubleColon() throws IOException
      {
          int c = skip_over_whitespace();
          if (c != ':') {
              unread_char(c);
              return false;
          }
          c = read_char();
          if (c != ':') {
              unread_char(c);
              unread_char(':');
              return false;
          }
          return true;
      }
docs: peeks into the input stream to see if the next token
  would be a double colon.  If indeed this is the case
  it skips the two colons and returns true.  If not
  it unreads the 1 or 2 real characters it read and
  return false.
  It always consumes any preceding whitespace.
  @return true if the next token is a double colon, false otherwise
  @throws IOException