Is this a non-standard attribute?

We wanted web pages to control the spellchecking defaults to some degree. For example, webmail applications will want to automatically turn it on for subject lines, even though it is normally off for <input> elements.

We discussed with the WHATWG web standards group to come up with the attribute. I'm not sure about the status of this in any of their specs, as I'm not sure there was any strong consensus. That's one of the problems coming out with a new feature not currently supported in any other browser or mentioned in any standards.