xml percent

Hi,

I would like to construct a percent schema type, which is a double value 
between 0.0 and 100.0, with a "%" character at the end.  For example 
"39.8%".

Does anyone know how I could specify such a type in an xsd file?

Ideally it would be nice to support any double number (including those with 
an exponent) in front of the % symbol, if that is possible...

Thanks,
Tony