Gecko supports these.

WebKit has not moved on these https://bugs.webkit.org/show_bug.cgi?id=91463 (despite developers wanting it) and Chromium hasn't either https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/bChX6leKqtg/Idut6cE4ORcJ. There appears to be some sort of support for this in the Chromium camp, if this was more of a local notification rather than a global one.

We have these options:

• Keep them, and add their corresponding on* attributes which Gecko already ships
• Replace them with something else (what?)
• Remove them