Return the user field of a mapping
USERFIELD = GETUSER(W,FIELD,SUB)
If the requested field does not exist USERFIELD = ;
Note the the USER field of mappings was originally intended for a user defined description of mappings. Later its usage was extended to a field for storing general information on mappings. For that reason 'old' mappings without a structure in the user field are transformed such that this information is stored in a subfield USER in the user field. It can be retrieved by GETUSER(W).