diff --git a/Procedural-cosmetic-filters.md b/Procedural-cosmetic-filters.md
index 3bfec05..b6e81a5 100644
--- a/Procedural-cosmetic-filters.md
+++ b/Procedural-cosmetic-filters.md
@@ -35,4 +35,8 @@ The `:has(arg)` operator is actually a planned pseudo-class in CSS4, but as of w
 - Examples:
     - `mobile.twitter.com##main [role="region"] > [role="grid"] > [role="rowgroup"] [role="row"]:if(div:last-of-type span:has-text(/^Promoted by/))`
 
-The purpose of `:if(...)` ressembles the purpose of the `:has(...)` operator, however the difference is that the argument for the `:has(...)` operator **can not** be anything else than a plain CSS selector. This limitation to the `:has(...)` operator is to ensure that they will be able to be implemented declaratively once a browser supports `:has(...)` as a valid CSS4 selector.
\ No newline at end of file
+The purpose of `:if(...)` resembles the purpose of the `:has(...)` operator, however the difference is that the argument for the `:has(...)` operator **can not** be anything else than a plain CSS selector. This limitation to the `:has(...)` operator is to ensure that they will be able to be implemented declaratively once a browser supports `:has(...)` as a valid CSS4 selector.
+
+### `subject:if-not(arg)`
+
+Essentially the same as the `:if(...)` operator, except that the element _subject_ is selected if the result of evaluating _arg_ is zero elements.