code: func (n *node) sizeLessThan(v int) bool {
  	sz, elsz := pageHeaderSize, n.pageElementSize()
  	for i := 0; i < len(n.inodes); i++ {
  		item := &n.inodes[i]
  		sz += elsz + len(item.key) + len(item.value)
  		if sz >= v {
  			return false
  		}
  	}
  	return true
  }
docs: // sizeLessThan returns true if the node is less than a given size.
  // This is an optimization to avoid calculating a large node when we only need
  // to know if it fits inside a certain page size.