Naming for the *attribute* to enable "light dismiss for dialog"

[mfreed7]

See #950 for the first incarnation of this poll. After some additional discussion in WHATWG, we've coalesced around an attribute with multiple values, such as:

• <dialog attribute_name=none> - no automatic closing at all
• <dialog attribute_name=closerequest> - closes via ESC (or any such close signal)
• <dialog attribute_name=any> - closes via ESC or clicking outside the bounds of the dialog

This poll is about "attribute_name" in the above list. What should that attribute be called?

[GrimLink]

In general, I would recommend using closedby as it is the most concise, memorable, and easy-to-understand option. However, if you want to emphasize the idea of initiating a closing mechanism, then closetrigger is a good choice. Avoid using autoclose unless you specifically want to imply that the closing process occurs autonomously.

[Link2Twenty]

Would these triggers fire both close and cancel? Using the close keyword makes it feel like cancel wouldn't be fired, maybe dismissby?