wp-includes/deprecated.php:2843Checks if the current user belong to a given site.
$blog_idintoptional0boolfunction is_blog_user( $blog_id = 0 ) { _deprecated_function( __FUNCTION__, '3.3.0', 'is_user_member_of_blog()' ); return is_user_member_of_blog( get_current_user_id(), $blog_id );}Introduced in MU (3.0.0). Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/deprecated.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.