Actually, I spoke to soon. Since selector engines work right to left, this would first narrow down the list of elements to all the spans in the document. Assuming thats a fairly small percentage of the overall tags in the document, this selector runs at .0023 ms on my MBP w/ 8 GB or RAM.

Sa'll good.

Edit: For the record, bGriz edited his comment, making my comment invalid.

Edit (2): Thanks!

Yea, thats slower for sure.