Using WordPress ‘is_main_network()’ PHP function
Determines whether a network is the main network of the Multisite installation.
HTTPS
Using WordPress ‘is_main_blog()’ PHP function
Deprecated functionality to determin if the current site is the main site.
Using WordPress ‘is_local_attachment()’ PHP function
Determines whether an attachment URI is local and really an attachment.
Using WordPress ‘is_login()’ PHP function
Determines whether the current request is for the login screen.
Using WordPress ‘is_lighttpd_before_150()’ PHP function
Determines whether the server is running an earlier than 1.5.0 version of lighttpd.
Using WordPress ‘is_404()’ PHP function
Determines whether the query has resulted in a 404 (returns no results).
Using WordPress ‘iso8601_to_datetime()’ PHP function
Given an ISO 8601 (Ymd H:i:sO) date, returns a MySQL DateTime (Y-m-d H:i:s) format used by post_date[_gmt].
Using WordPress ‘iso8601_timezone_to_offset()’ PHP function
Given an ISO 8601 timezone, returns its UTC offset in seconds.
Using WordPress ‘in_category()’ PHP function
Checks if the current post is within any of the given categories.