When copying, the text/plain register is populated with the textBetween of the selected fragment… however, there is no way to specify what a given node should return for textBetween.
We have a “block link” node, which stores an href attribute. When copied, these nodes disappeared from the plaintext representation, which made it less interoperable with programs that don’t use the html clipboard. We ended up converting the node into an atomic text-containing node, and storing the href as text content of this node.