code: public static String stripExpressionIfAltSyntax(ValueStack stack, String expr) {
      if (altSyntax(stack)) {
        // does the expression start with %{ and end with }? if so, just cut
        // it off!
        if (expr.startsWith("%{") && expr.endsWith("}")) { return expr.substring(2, expr.length() - 1); }
      }
      return expr;
    }
docs: If altsyntax (%{...}) is applied, simply strip the "%{" and "}" off.
  
  @param stack
  the ValueStack where the context value is searched for.
  @param expr
  the expression (must be not null)
  @return the stripped expression if altSyntax is enabled. Otherwise the
  parameter expression is returned as is.