inputmode syntax question

Hi all,
I'm working with the MWI Best Practices Working Group and had a quick
question about valid inputmode syntax. As a bit of background, we're writing
a test as part of our mobileOK Basic checker that assesses the use of the
input mode attribute.

Can a single modifier token, such as "digits" be used as a value for
inputmode, or must it always be preceded by a script token?

After looking at the specs on XHTML Basic 1.1, it seems as if the modifiers
must always follow a script token, and cannot be a stand alone value.

Thanks in advance, and I look forward to your input.

Cheers,
Laura