New #ajax 'prevent' property added.

A new #ajax['prevent'] property was added, defaulting to 'click'.

Binding to 'mousedown' rather than 'click' means that it is possible to trigger a click by:

1. Pressing the mouse button
2. Holding the mouse button down until the Ajax request is complete and the button is re-enabled.
3. Then releasing the mouse button.

Setting the 'prevent' property makes ajax.js bind an additional handler to prevent such a click from triggering a non-Ajax form submission. This also prevents a textfield's <Enter> keypress from triggering this button's non-Ajax form submission behavior.

See:

#ajax on Forms API reference

Ajax Framework