Variable variables are considered unused when only appearing on the left-hand side of an assignment. This is considered fine: ```php function fn() { $foo = true; $var = 'foo'; return $$var; } ``` While this says `$var` is unused: ```php function fn() { $foo = true; $var = 'foo'; $$var = false; } ``` (`$foo` is marked unused in both cases, but I guess there's no way to avoid that without deeper program flow analysis.)