Link
Class.
A link: a URL entered freely or a post, term or media file chosen in a
search, plus whether it opens in a new tab. Edited with the link control of
the block editor (a search form on the settings page and in classic meta
boxes); in blocks it counts as content. Never null: an empty URL means no
link. Templates print it with link_attributes().
A linked object is stored with its ID; when the value is created, the URL becomes the current URL of the object, or empty if the object no longer exists or is not public (renders for the block editor keep objects that are not public, so editors see their choice). The stored URL of a linked object is only what the editor showed when it was chosen.