[relax-ng] Optional quotes?

I have occasionally found myself writing things like

  xs:string { length = 1 }

instead of

  xs:string { length = "1" }

which led me to wonder whether it would be worth allowing the former case,
by reviving the SGML rule (also used extensively in HTML) that quotes are
optional when the value is an NMTOKEN.  This rule could be applied in
parameter lists and perhaps also in attribute values in annotations.

I am not sure if this is worth doing.  What to other people think?

James