You mean a way to filter in or out readonly inputs in a form inside a selector?

If so, you can do this like this already:

i.e.:

// To select all readonly inputs in form with id "form_id"
$("#form_id input[readonly='readonly']").serialize();

// To select all inputs BUT readonly ones
$("#form_id input[readonly!='readonly']").serialize();

Look at the attributes section of this page for more details: http://docs.jquery.com/Selectors

See above for the solution. Adding new pseudos isn't a good idea because they throw console warnings in Firefox / Safari / Chrome due to the use of querySelectorAll.