Using WordPress ‘is_year()’ PHP function
Determines whether the query is for an existing year archive.
HTTPS
Using WordPress ‘is_wp_error()’ PHP function
Checks whether the given variable is a WordPress Error.
Using WordPress ‘is_wpmu_sitewide_plugin()’ PHP function
Deprecated functionality for determining if the current plugin is network-only.
Using WordPress ‘is_user_spammy()’ PHP function
Determines whether a user is marked as a spammer, based on user login.
Using WordPress ‘is_user_option_local()’ PHP function
Check whether a usermeta key has to do with the current blog.
Using WordPress ‘is_user_member_of_blog()’ PHP function
Finds out whether a user is a member of a given blog.
Using WordPress ‘is_user_logged_in()’ PHP function
Determines whether the current visitor is a logged in user.
Using WordPress ‘is_user_admin()’ PHP function
Determines whether the current request is for a user admin screen.
Using WordPress ‘is_upload_space_available()’ PHP function
Determines if there is any upload space left in the current blog’s quota.