How to make validation of Widget.render method?

Question

Django

From documentation:

render(name, value, attrs=None)
Returns the HTML for the widget as a Unicode string. This method must be implemented in child classes. Otherwise, a NotImplementedError exception will be thrown.
No one guarantees that the received value will be correct, so the implementation of the method in child classes must provide appropriate validation.

What kind of check should be done here? Right now I'm just returning a line of html code

Answer 1

Apparently it means that value is not necessarily the correct value of the desired type. For example, a date widget may receive a number.