This is a fair point. The underlying instrumentation here is based on the matching of CSS rules to the DOM via selectors. We then map those rules back into sour

This is a fair point. The underlying instrumentation here is based on the matching of CSS rules to the DOM via selectors. We then map those rules back into source locations (including external style sheets, @sourceURL, and style tags). We do also have to account for all the other bytes in the block of CSS. I believe in your case, these bytes are all whitespace. Here's a basic comparison of two pages where all rules are used: http://imgur.com/ZtfNFmo http://imgur.com/ZtfNFmo On the left, we have typical whitespace; On the right: no extra whitespace between style tags and rules. You can see we went from 15 unused bytes to 0. To be extra clear about this we could somehow indicate these bytes are "unused whitespace" bytes. The implication is a little different in that case, mostly just to use a minifier. (I work on these tools)