This seems to be an attribute only supported on older versions of IE and never standardized. The modern, cross-browser CSS property to accomplish this is via user-select: none

Indeed.

Perhaps, this would be out of scope for caniuse.com, but IMHO it would be super useful to be able to find such an explanation when searching for such a not standard (and even deprecated) attribute. 😅

If out of scope, please feel free to close this issue. 🙂

Not out of scope, but not high on the priority list either. Will keep it open in case other folks run into it.

I just randomly found the unselectable attribute in our project and wondered what in the world this absolutely undocumented thing is supposed to do.

Would be great to at least get a dummy-ish entry on caniuse.

I was able to find out that Edge/IE11 mode apparently respect the attribute on text-element. Apparently also older Opera Versions make use of this attribute.

Some documentation I found: help.dottoro.com/lhwdpnva.php