Retrieve all of the post categories, formatted for use in feeds.

Retrieves the ID of the current item in the WordPress Loop.

Retrieve the date on which the post was last modified.

Retrieves theme modification value for the active theme.

Displays header image URL.

Displays the custom header text color in 3- or 6-digit hexadecimal form (minus the hash symbol).

Determines whether WordPress is already installed.

Is the query for the robots.txt file?

Checks whether the given variable is a WordPress Error.

Displays the language attributes for the ‘html’ tag.