Add missing documentation for the `xmlrpc_element_limit` hook in wp-includes/class-IXR.php.

Props ankitgadertcampcom, kpdesign.
Fixes #29977.


git-svn-id: https://develop.svn.wordpress.org/trunk@30744 602fd350-edb4-49c9-b593-d223f7449a82
Document the default arguments for `register_sidebar()` in the hash notation style.

Props coffee2code.
See #28298.


git-svn-id: https://develop.svn.wordpress.org/trunk@30745 602fd350-edb4-49c9-b593-d223f7449a82