code: protected static boolean isNestable(String expression) {
          return !(expression.contains(SearchExpressionConstants.ALL_KEYWORD)
                  || expression.contains(SearchExpressionConstants.NONE_KEYWORD)
                  || expression.contains(SearchExpressionConstants.PFS_PREFIX));
      }
docs: Checks if the given expression can be nested. e.g. @form:@parent This should not be possible e.g. with @none or @all.
  
  @param expression The search expression.
  @return <code>true</code> if it's nestable.