Royal TSX already finds <button> elements in the DOM as long as they have some kind of identifying attribute. Any one of these works:
Without any of those attributes we're unfortunately not able to build a jQuery selector matching the specific element and so we don't show the element in the combo box.
Would you like me to assist there? You can use a selector by order number. jQuery('INPUT[type="submit"]:not([name]):eq(XX)') where XX is the order number of the button.
Well, yes, there are multiple ways to achieve this but I don't think any of them is robust enough to build it into the app. I also played with the thought of using ":contains" but as with your approach, that's very fragile in regards to DOM changes.
If we exclude a highly unlikely event that unnamed submit buttons of the login form get reshuffled on each page load, the only time they can change their order in DOM is a redesign / remake of the web site. In which case anything can change, including name, id and the whole form.
If a form has a submit button like <button type="submit">Log in</button> it does not appear in the list of elements in Autofill settings. Maybe at some point in the future it might be worth adding support for such elements, presenting them in the drop down by the inner text, or, if empty, just like "<submit button>" for example.
Alternatively/additionally, a form submit action would be nice to have there.