Arrived here from @brucelawson's 10/12/19 post (https://www.brucelawson.co.uk/2019/checklist-to-avoid-the-most-common-accessibility-errors/) where he recommends this bookmarklet for checking certain common accessibility errors.
Similar to the issue he logged (#25), is the “Forms must have action attributes” still relevant?
HTML5 spec https://www.w3.org/TR/html52/sec-forms.html#element-attrdef-submitbuttonelements-formaction:
The action and formaction content attributes, if specified, must have a value that is a valid non-empty URL potentially surrounded by spaces.
'If specified' as in 'optional'? This answer on StackOverflow seems to think so (https://stackoverflow.com/questions/9401521/is-action-really-required-on-forms). According to them it was required in HTML4 but not in HTML5 and can be left off. So if doctype is HTML5 there is no need for the action attribute?