\WP_User Object | What's the Difference Between {caps} and {allcaps}?

Question

Upon dumping the \WP_User object, I've noticed that there are two properties, which are directly related to capabilities for a particular user.

1. $user_object->caps
2. $user_object->allcaps

I've instantly noticed that there's less array values for $user_object->caps than there are in $user_object->allcaps. Likely hence the naming convention here.

I currently only observe ONE value under $user_object->caps. I also have a custom role assigned to this user. The one value in $user_object->caps happens to be the name of my custom user role. However, that very same value is also listed in $user_object->allcaps.

1. What's the difference between the two properties $user_object->caps and $user_object->allcaps?
2. Is there ever a situation where the capabilities listed in $user_object->caps WOULDN'T be found under $user_object->allcaps?
3. Is there any reason I would need to use $user_object->caps or can I rely on checking $user_object->allcaps for a particular user?

Answer 1

Examining the comments for the properties in the WP_User class reveals that allcaps is:

All capabilities the user has, including individual and role based.

And caps is:

The individual capabilities the user has been given.

But you probably shouldn't be using the properties directly. WP_User has a has_cap method that should be used instead, as it checks the appropriate properties and runs the result through the relevant filters.