Labels are added to the sources when withlabels=`yes'. The source of information about labels is controlled by the parameter labelstyle. This parameter works in a fashion identical to ncutsortstyle (see subsection 3.4). The accompanying expression parameter is labelexpression. This expression may be any arithmetic combination of source-list columns which yields a numeric result, or it may be the name of a string-valued column.
At present, only integer values are permitted as source labels, so if labelstyle=`expr' the column indicated in labelexpression must be an integer-valued one. In future it is intended to allow any alphanumeric column value to be used. The parameter interface for labels may at that point be expanded or modified slightly.
The colour, text size and line thickness of the source circles and labels may be specified via the parameters srccolour, labelsize and thickness.