Formalization of rule 91

Hi,

Rule 91 [1] can be formalized saying:

//select[let $ff:=self::node() return 
count(//label[@for=$ff/@id]) != 1] = ()

PS: In other words, every select (which we name with a variable), must 
have one associated label, i.e., one label whose "for" attribute equals 
the "id" attribute of the select).

PS2: There are over 60 formalized tests (using XPath and XQuery) at 
http://www.it.uc3m.es/vlc/wai/checks.xml .

[1] http://www.w3.org/WAI/GL/WCAG20/tests/test91.html

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