prefer-button rule disallows <input type="submit"> as well
Markup in a form in an otherwise valid document such as <input type='submit' name='submit' value='Search'>
will be declared invalid by html-validate for violating the "prefer-button" rule. While it seems valid to complain about the use of input type="button" and recommend the use of the button element instead, I don't think disallowing input type="submit" wholesale is the correct recommendation.