min and max for strings: are they literals or references?

Greetings all,

I was wondering if someone could clear this up for me:

XMLSchema doesn't define the min and max facets for 
elements, yes? XForms does, however. So what is the meaning of:

<string name="foo" min="bar">
<string name="bar">

Does the text of element foo have to be >= element bar, or 
 >= "bar"?