docs: private boolean speculateFullAnnotation() {
          state.backtracking++;
          int start = input.mark();
          try {
              exprParser.fullAnnotation( null );
          } catch ( RecognitionException re ) {
              System.err.println( "impossible: " + re );
              re.printStackTrace();
          }
          boolean success = ! state.failed;
          input.rewind( start );
          state.backtracking--;
          state.failed = false;
          return success;
  
      }