Brackets generally doesn't code-hint things that are deprecated in HTML 5. Consider replacing cellspacing, etc. with more modern CSS alternatives. If you can't do that, here are a couple other suggestions...
If you run Brackets directly from source, then you can just directly modify the HtmlAttributes.json file that controls the code hints.
A more flexible solution would be to write an extension that adds these attributes to the built-in code hints. Unfortunately, code hint extensibility is currently somewhat limited in Brackets: you can only replace the HTML hint provider, not add to its results. You could fork the built-in "HTMLCodeHints" extension that's in the Brackets source, modify its copy of HtmlAttributes.json, and increase its priority (3rd argument to CodeHintManager.registerHintProvider()
) so that it replaces the built-in copy. But it's debatable whether that's any cleaner than just running from a patched copy of the source.
So the truly ideal solution -- a small extension that just adds a few new properties to the existing set of hints -- isn't possible today. I've created a user story in the Brackets backlog in the hopes that it will eventually become supported: Code Hints extensibility: consolidate results from multiple providers.