wp-includes/class-wp-roles.php:293Determines whether a role name is currently in the list of available roles.
$rolestringbool public function is_role( $role ) { return isset( $this->role_names[ $role ] ); }Introduced in 2.0.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-roles.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.