If you have several submit elements (inputs or buttons with type="submit") that each cause different things to happen (e.g. you might have a button that sends an extra attribute) you might run into trouble when submitting the form by pressing the return key in a field.

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When nothing fancy like a tabindex is defined it seems as if the first submit element inside a form is chosen (and has its attributes submitted) when pressing return.\
So, if possible, put your "default" (aka least harmful) submit element before others.

NB: If you submit a form via JavaScript none of the buttons' attributes will be submitted.