Clarify how to use the `compat_features` key

[autonome]

The contribution guide says this key is optional, and has the following description:

The list of browser-compat-data entries that make up this feature. In many cases, the corresponding browser-compat-data entries already map to the feature ID, and this is therefore not needed.

Does this mean there are times where there's a disjoint between the two? In that case, do you list them all or only the missing ones?

And if there are missing ones, should suggest to file a BCD issue?

[ddbeck]

Does this mean there are times where there's a disjoint between the two? In that case, do you list them all or only the missing ones?

The gist is that the contents of the authored YAML file (i.e., <feature-id>.yml) overrules other possible sources of data. This goes for status as well. If you provide a compat_features value, then the BCD tag is completely ignored. So either provide a complete compat_features list or none at all.

I've opened #1667 to improve that table entry.

And if there are missing ones, should suggest to file a BCD issue?

No, that's not necessary. Open Web Docs is working on synchronizing compat_features keys with BCD's tags (e.g., #1622). That work is partly tracked with openwebdocs/project#208, but I'm putting it on my to-do list now to get some issues in web-features to correspond to that.

[Elchi3]

#1668 is an example for authoring an override (which we will sync back to BCD automatically soon)