Feature Request: Blacklist for Richtext elements

I was happy to find the whitelister hook for richtext elements, but a bit disappointed that I could not blacklist elements, which is much more important for me having users copying stuff from word and who knows what… Instead of having a blacklister, it would be also ok to have an option to overwrite the original whitelist, not merge it…

In reality it seems not such a big problem, unless you copy html directly into your chrome dev tools richtext html field, but I want to make sure…

Also a way to replace html elements would be great, for example the <b> and <i> tags from hello js with <strong> and <em>

[gasman]

Yep, I think this is fully covered by rich text features, as of #4079.

[gasman]

It looks like it should be possible to ‘blacklist’ an element with the following code (untested):

def reject_tag(tag):
    tag.unwrap()

@hooks.register('construct_whitelister_element_rules')
def whitelister_element_rules():
    return {
        'h1': reject_tag
    }

You could probably use something similar to replace the tag with another one (although, if I recall correctly, the HTML spec specifically advises that HTML authoring tools shouldn’t replace <i> with <em> unless they’re absolutely certain that the author intended it as emphasis, rather than, say, a book title.)

I agree we ought to make this easier, though. (I’m surprised that the requirement to remove elements from the whitelist hasn’t come up before - I guess most people aren’t really on board with the Wagtail philosophy of taking flexibility away from editors 😃 ) A couple of easy ways to do that:

1. provide the above reject_tag method in wagtail.wagtailcore.whitelist, alongside allow_without_attributes
2. in https://github.com/torchbox/wagtail/blob/ba807e5f45812e85bf83b49bf04d2c796ef63cda/wagtail/wagtailcore/whitelist.py#L136-L144, treat a None or False rule the same way as a KeyError (so that the above code could be simply return {'h1': False}).