Return the current node's document number as a string. If the second optional argument is true, then return the document number as a longer description rather than a code. That is, as `Starlink Cookbook n' rather than `SC/n'
If present, this indicates which grove is to be used to find the document element.
If true, return a longer descriptive string rather than a code.
Type: string
The document number as a string, or #f
if docnumber isn't defined.