code: def start_range(self):
        
        if len(self._exons) == 0: return None
        return GenomicRange(self._exons[0].chr,
               min([x.start for x in self._exons]),# must be part of junction
               max([x.start for x in self._exons]))
docs: Similar to the junction range but don't need to check for leftmost or rightmost