The accuracy of this estimate might once be very good, thus its in basepairs. Yet for the time being the start-value is of not big scientific content, a mere drawing aid. The length can be assumed to be more reliable. If no arguments then default contig should be that raw contig containing the middle base for the entire FPCcontig and default orientation is 1. Specially useful, if you got your clone by its name and want to go back to the contig.
Length is considereable more trustable than start.
There is a chance that there is none, when the in silico digest cannot successfully be mapped back to an original clone name. Returns zero length list otherwise. For building virtual contigs, it might be convenient to have a function returning neighbouring clones to a given one.