code: private void evaluateExpressions() throws JspException {
  
          // 'value' attribute (mandatory)
          value = ExpressionEvaluatorManager.evaluate(
                  "value", value_, Object.class, this, pageContext);
  
          // 'variant' attribute (optional)
          if (variant_ != null) {
              variant = (String) ExpressionEvaluatorManager.evaluate(
                      "variant", variant_, String.class, this, pageContext);
          }
      }
docs: Evaluates expressions as necessary