Mutation observer for attributes. Maybe.

[gorhill]

Not decided whether I will implement this, depends how much not having this causes issues.

For instance, normally uBlock should have been affected as well by the issue raised there: https://adblockplus.org/forum/viewtopic.php?f=2&t=25103.

But it is not, because the attribute title is set after the node is added to the DOM. Although in this case it was a blessing, I suspect it may well happen that some cosmetic filters are not enforced because an attribute on which a specific filter depends may be set after a node is added (the current mutation observer only look for added nodes).

This would need careful implementation to minimize as much as possible the added overhead.