Prevent single-input forms from submitting when the user hits Enter, unless the input includes the `submit13` class.

submit13.js

// prevent all forms from submitting on pressing Enter in an input
// unless the input specifies the `submit13` class.
$("input").on("keypress", function(e) {
	if (e.which == 13) {
		// prevent all first, and trigger manually to bypass the quirk
		// where browsers will submit single-input forms on pressing Enter.
		// otherwise two submit events would be generated in quirk cases.
		e.preventDefault();
		if ($(this).is(".submit13")) {
			$(this).closest("form").trigger("submit");
		}
	}
});