The CSS Object Model.

HTML comments are basically just a HTML tag that isn't rendered. Tools that 'compile' the HTML code into a document tree, including browsers, preserve comments as nodes without any extra effort.

CSS comments can go anywhere:

    /*wow*/ .selector /*x*/ {animation /*z*/: 2s /*z*/ linear /*z*/ bounce;}

Tools that transform/parse CSS can either: 1. Strip comments before parsing, meaning anything based on the parsed version will lose the comments. 2. Dedicate a disproportionate amount of complexity to retaining the comments, and still not really have a good way to handle them through edits/transformations.