What is is_continuous?

### Description

In the rules I see `is_continuous` which cannot be found clearly in the documentation, except in the Changelog. I cannot see it used anywhere (although the thing it was renamed from `only_known_words` pops up in one script, weird) so I am wondering if this was removed, if the documentation is simply incomplete or if something else is going on.

### Select Category

- [X] Inconsistency
- [ ] New Section Request
- [ ] General Improvement
- [ ] Typo/Mistakes
- [ ] Other