Setting rules for tabs, e.g. you can set a tab to be triggered only when needed, by a shortcut key.
Or what code principles should be followed for the complementary information, which can be written in the rules
For example: more security and no vulnerabilities,
Use case would be avoiding hallucinations like generating links when typing some markdown
If Cursor team is worried about potentially increased context lengths, they can limit the .cursortabrules entries to a max number of tokens.
This feature is crucial, especially for programming language designers.