def function(self, rule, args, **kwargs):
        """
        Callback method for rule tree traversing. Will be called at proper time
        from :py:class:`pynspect.rules.FunctionRule.traverse` method.

        :param pynspect.rules.Rule rule: Reference to rule.
        :param args: Optional function arguments.
        :param dict kwargs: Optional callback arguments.
        """
        return '<div class="pynspect-rule-function"><h3 class="pynspect-rule-function-name">{}</h3><ul class="pynspect-rule-function-arguments>{}</ul></div>'.format(rule.function, ''.join(['<li class="pynspect-rule-function-argument">{}</li>'.format(v) for v in args]))