In https://github.com/ezsystems/ezpublish-kernel/pull/1926 a new naming has been proposed, and we need to reflect this on the setting as well.
Given custom tags have not been exposed yet in the product we can do this, but we should still add a BC note + upgrade note about the change.
Suggestion for discussion for this milestone:
1. Implied in suggested config structure there might be a custom template tag and custom docbook tag with same name, so we need to check if that is ok at all (this will for instance be an issue if there is a general block about adding classes to tags, or a need to identify tags by name if it does not get prefixed somehow)
2. For output rendering, how to handle custom php logic when needed? (check how it is done currently and how it might be made extendable if it isn't already)
3. Definition of custom attributes, and the implications that it should be used for server side validation before xsl transformation to storage format.
4. Config for CSS for the tags would be needed to have some configuration somewhere, but might not be needed if it can be already done by registering css/js to be loaded using existing platform ui config