code: func StartBlock(startBlock *waddrmgr.BlockStamp) RescanOption {
  	return func(ro *rescanOptions) {
  		ro.startBlock = startBlock
  	}
  }
docs: // StartBlock specifies the start block. The hash is checked first; if there's
  // no such hash (zero hash avoids lookup), the height is checked next. If the
  // height is 0 or the start block isn't specified, starts from the genesis
  // block. This block is assumed to already be known, and no notifications will
  // be sent for this block. The rescan uses the latter of StartBlock and
  // StartTime.