code: static boolean isMixedExpression(String expression) {
  
          if (null == expression) {
              return false;
          }
  
          // if it doesn't start and end with delimiters
          return (!(expression.startsWith("#{") && expression.endsWith("}")))
                    && isExpression(expression);
  
      }
docs: /*
  Determine whether String is a mixed value binding expression or not.