Extend HTML tags

How to extend html language tags? I would like to add custom html tags for autocomplete to work:

<foo-bar custom-attr="bar"></foo-bar>

The HTML completer is currently using a fixed set of tags, and since I expect this use case to be rare, I’m not really that interested in creating a public interface for reconfiguring it. Maybe the best way forward would be to fork the code in lang-html/src/complete.ts and adjust it for your purpose.

The use case is to provide autocomplete for custom WebComponents tags, attributes.