WordPress at a glance
function is not described

WP_Theme::is_allowed() public WP 3.4.0

Whether the theme is allowed (multisite only).

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

No Hooks.

Return

true/false. Whether the theme is allowed for the network. Returns true in single-site.

Usage

$WP_Theme = new WP_Theme();
$WP_Theme->is_allowed( $check, $blog_id );
$check(string)
Whether to check only the 'network'-wide settings, the 'site' settings, or 'both'.
Default: 'both'
$blog_id(int)
Ignored if only network-wide settings are checked.
Default: current site

Changelog

Since 3.4.0 Introduced.

Code of WP_Theme::is_allowed() WP 5.5.1

<?php
public function is_allowed( $check = 'both', $blog_id = null ) {
	if ( ! is_multisite() ) {
		return true;
	}

	if ( 'both' === $check || 'network' === $check ) {
		$allowed = self::get_allowed_on_network();
		if ( ! empty( $allowed[ $this->get_stylesheet() ] ) ) {
			return true;
		}
	}

	if ( 'both' === $check || 'site' === $check ) {
		$allowed = self::get_allowed_on_site( $blog_id );
		if ( ! empty( $allowed[ $this->get_stylesheet() ] ) ) {
			return true;
		}
	}

	return false;
}