Suggestion:
Add an option to the validator to hide errors caused by custom tags (and also custom attributes).

Use case:
Pages created in Angular typically show lots of errors caused by custom tags used for Angular directives (like <my-directive>...</my-directive>) and custom attributes (like ng-click="..." etc.)
(Note, on Angular pages I copy & paste generated code into the validator)

I'm aware that it is possible to write Angular code in such a way that there are no parsing errors (e.g. <my-directive> could be replaced by <div data-my-directive>) but unfortunately this is usually not the case.

Currently, when the validator comes across a custom tag I get an error similar to this:
"Element my-directive not allowed as child of element body in this context. (Suppressing further errors from this subtree.)"

The biggest issue for me is that the sub tree is not validated.
I have pages where a custom tag is used for the main content of the page, so effectively nothing on the page is validated.

I want to be able to ignore the errors caused by Angular (custom tags and attributes) and see structural problems (incorrect nesting, duplicated id's etc). Currently that's not possible if errors are in a sub tree that's ignored.
To address this, I think the easiest solution would be an option to hide custom tags and attributes. 

Note, the existing "message filtering" cannot be used in this scenario, because the sub tree of a custom tag would still be ignored, and therefore large parts of the page may be excluded from the validation.