... if used more than once in a function/mixin Stupid example: ``` @function double-value($value) { @return $value * 2; } @mixin doubledouble($attribute, $value) { #{$attribute}: double-value($value) + double-value($value); } ``` Will state that `doubledouble` requires` double-value` 2x I will try to look into this as soon as I find the time.