The documentation specifies that
:submit: Specifies the DOM element ID thatâÂÂs used as the parent of the form elements. By default this is the current form, but it could just as well be the ID of a table row or any other DOM element.
However, with the 1.2 RC1, this does not work with non-form elements anymore. This may or may not be related to Changeset [5449]
Either this is intended, in which case the documentation needs to reflect this and it needs to be documented, since a lot of code is likely to break with this change, or the ruby code needs to be adapted to reflect the changes in the prototype library.