A question about the `liftTarget` function

I’m puzzled about the underlying reasoning behind choosing the depth that a NodeRange could be lifted to.

Assume we need to lift the second paragraph “cd” out of the block quote:


We need to call liftTarget(range) where range covers the <p>cd</p> node.

export function liftTarget(range) {
  let parent = range.parent
  let content = parent.content.cutByIndex(range.startIndex, range.endIndex)
  for (let depth = range.depth;; --depth) {
    let node = range.$from.node(depth)
    let index = range.$from.index(depth), endIndex = range.$to.indexAfter(depth)
    // line 21
    if (depth < range.depth && node.canReplace(index, endIndex, content))  
      return depth
    if (depth == 0 || node.type.spec.isolating || !canCut(node, index, endIndex)) break

When the execution reaches line #21, the local variables are:

range.depth = 1

depth = 0

content = <p>cd</p>

node = the root “doc”

index = 0, endIndex = 1

Ofc, node.canReplace(index, endIndex, content) would return true, but I wonder how could that alone indicate we can lift the <p>cd</p> to be a child of the root node?