Formalization of rule 58

Hi,

Rule 58 [1] seems not to be complete. It says that all inputs whose type 
is "image" should have an alt attribute, but it should also say that all 
inputs whose type is different from "image" must not have an alt 
attribute.

In other words:

//input[@type="image"][not(@alt)] = ()

but also

//input[@type!="image"][@alt] = ()

Should it be a different test?

[1] http://www.w3.org/WAI/GL/WCAG20/tests/test58.html

Vicente Luque Centeno
Dep. Ingeniería Telemática
Universidad Carlos III de Madrid
http://www.it.uc3m.es/vlc