This module would be a lot easier to figure out if there were (a) documentation of the appropriate syntax to use here on drupal.org, either this module's page or the main documentation, and (b) better explanation of syntax on the module's configuration page. It took way too much trial and error for me just to figure out how to exclude the home page configuration on the site I'm currently building. The related issue "I can't get this to work" is another example for the need to document syntax.
Perhaps the syntax used is standard for how Drupal's config system works, but unfortunately I have been unsuccessful finding documentation that explains it. If such documentation exists, simply linking to it would be a good start, though I suspect that a bit more text/clarification would make life easier for people to get up to speed with this module.
What do the different separators (period vs. semicolon) represent and when do you use each? What is the relationship between config export filenames, the configs therein, and the way you would specify things to ignore at different levels? The module's configuration page doesn't touch on ignoring a single configuration setting until the very last item, user.mail:register_no_approval_required.body and it still fails to explain what parts use periods and what parts the semicolon. (It's also a very unreadable configuration file to ask someone to try to read to pick up structure and context.)
My recommendation would be to provide a bit more context for the deep layers of organization in configuration entity settings beyond what is already on the module's configuration page. For example:
- user.settings (will ignore all settings in the user.settings configuration entity, which can be found in user.settings.yml)
- system.site:page.front (will ignore just the home page setting in the system.site configuration entity, found in system.site.yml; note that the settings are separated from the config entity by a semicolon)
- etc.
The system.site config entity would be a lot easier to read than the user.mail config entity, while still being familiar.
And I'd still recommend adding something to the module page or drupal.org documentation explaining the syntax, with a link to more details, if available.
One last thing:
It would also be very helpful to provide some explanation of what the user should expect to see in the config sync UI or drush output when it's working right, because when you don't have your syntax correct, it's tough to know whether something is wrong and what you should be looking for to confirm that you got it right.
