The documentation could certainly be clarified to say that all decimals, as determined by isdecimal(), are also digits as determined by isdigit(). IMO the current documentation is confusing or wrong to stay that decimals ‘include digit characters’; it is actually the other way around.

I think it could also be clearer about how ‘general category “Nd” ’ and ‘the property value Numeric_Type=Digit or Numeric_Type=Decimal’ are related (if they are indeed related).