WordPress at a glance
function is not described

WP_Query::__isset() public WP 4.0.0

Make private properties checkable for backward compatibility.

{} It's a method of the class: WP_Query{}

No Hooks.

Return

true|false. Whether the property is set.

Usage

global $wp_query;
$wp_query->__isset( $name );
$name(string) (required)
Property to check if set.

Changelog

Since 4.0.0 Introduced.

Code of WP_Query::__isset() WP 5.7.2

<?php
public function __isset( $name ) {
	if ( in_array( $name, $this->compat_fields, true ) ) {
		return isset( $this->$name );
	}
}