Converting blocks lose anchor tags

[Clorith]

Describe the bug
When converting a classic page to blocks, any existing anchor tags on titles are lost. This is despite the block and the original classic content both utilize the id attribute to provide the anchor tag.

To Reproduce
Steps to reproduce the behavior:

1. Create a post in the classic editor
2. Edit the HTML of the post and add an anchor tag using the id attribute on a heading.
3. Save the post and leave
4. Open the post in Gutenberg
5. Choose to convert the post to blocks

Expected behavior
Elements that are supported in Gutenberg should be retained when converting, as an aside would it be an idea to not strip non-supported attributes but rather leave in the HTML to avoid breaking content?

Additional context
Gutenberg 3.0.1 (running on WordPress.org, in case there's something special introduced there?)

[danielbachhuber]

Related #6581 #6096 #4498

[danielbachhuber]

@WordPress/gutenberg-core Do we want to handle this with an abstraction similar to className, or should we simply add this feature to the blocks that it's relevant to? And, in either case, what should the attribute name be?

[brandonpayton]

It appears #8124 is meant to address this issue.

[Clorith]

#8124 only allows ID attributes, what about other attributes that users may have previously added manually for plugins and such for example?

We shouldn't be stripping anything when converting, if we do it should be a migration instead, and it should be clear that attribute data may be lost if it does not adhere to our pre-defined standards.

[brandonpayton]

👍 You're right. It just addresses a specific instance of this issue. Thanks for correcting.

[pento]

#8124 fixes the issue with the id attribute, #6878 continues the broader conversation of how to handle random attributes that we don't explicitly support.