wp-includes/class-wp-customize-manager.php:6123Callback for validating the external_header_video value.
$validityWP_Error$valuemixedmixed public function _validate_external_header_video( $validity, $value ) { $video = sanitize_url( $value ); if ( $video ) { if ( ! preg_match( '#^https?://(?:www\.)?(?:youtube\.com/watch|youtu\.be/)#', $video ) ) { $validity->add( 'invalid_url', __( 'Please enter a valid YouTube URL.' ) ); } } return $validity; }Introduced in 4.7.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-customize-manager.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.