An anchor represents a region of a hypertext document which is linked to another anchor in the same or a different document. We separate the first link from the others to avoid too many small mallocs involved by a list creation.
Most anchors only point to one place.
This one is for a new anchor being edited into an existing document. The parent anchor must already exist. This one is for a reference which is found in a document, and might not be already loaded. The anchor is only deleted if the corresponding document is not loaded. All outgoing links from parent and children are deleted, and this anchor is removed from the sources list of all its targets.