wp-includes/class-wp-icons-registry.php:364Checks if an icon is registered.
$icon_namestringbool public function is_registered( $icon_name ) { return isset( $this->registered_icons[ $icon_name ] ); }Introduced in 7.0.0. Unchanged from 7.0.4 through 7.1.0.
Signature, return type and hooks compared across 2 parsed releases.
src/wp-includes/class-wp-icons-registry.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.