code: private void evaluateExpressions() throws JspException {
          /* 
           * Note: we don't check for type mismatches here; we assume
           * the expression evaluator will return the expected type
           * (by virtue of knowledge we give it about what that type is).
           * A ClassCastException here is truly unexpected, so we let it
           * propagate up.
           */
  
          value = (String) ExpressionUtil.evalNotNull(
                  "url", "value", value_, String.class, this, pageContext);
          context = (String) ExpressionUtil.evalNotNull(
                  "url", "context", context_, String.class, this, pageContext);
      }
docs: /* Evaluates expressions as necessary