An un-activated Image Button submitter should add (0, 0) entries to the form data set

[jenseng]

If a form data set is constructed with a non-activated Image Button submitter, implementations include entries for the default coordinate (0, 0). However, the spec prose seems to imply that entries should not be included in this case, i.e. ... before this algorithm was invoked the user indicated a coordinate. The only way for the user to indicate a coordinate is by activating the input.

This ambiguity is normally a non-issue in conventional form submissions, since typically the submitter would have been activated. However, this may pose a problem for scenarios like someForm.requestSubmit(someButtonThatWasNotClicked) and the new submitter parameter to FormData, if users expect browsers to skip non-activated Image Button submitters.

To bring the spec in line with all implementations, the form construction algorithm prose should probably be reworded to default the coordinate to (0, 0) if the user hasn't selected one, and the Image Button activation prose could be similarly simplified.

• Further discussion here: Add FormData.constructor submitter tests web-platform-tests/wpt#37895 (comment)
• Simple repro using <form>.requestSubmit(...)