Rule: comment-style

[anderseknert]

Similar to how Go has ideas about what "doc comments" should look like (capitalized, sentence ending with period), it would be useful if Regal provided a way to enforce preferences on what metadata annotation values like title and description should look like. Since there's no established convention for that, we'll leave it up to the user to decide until there is one, and hence this rule should go in the custom category.

We should allow providing a regex that needs to match a given attribute, but perhaps also some pre-sets for the most common things like capitalization, periods, and whatnot.