Identifiers of document nodes.
Ids are short random strings ("Kq2b7Rt9Lm") that stay stable for the life of
a node: the CSS of a node is scoped to its id ([data-ex-id="Kq2b7Rt9Lm"]) and
the editor selects and moves nodes by id.
Summary
Functions
A new random id.
Whether id can be used as a node id: 1 to 40 letters, digits, - or _.
Anything else could break out of the attribute selectors the CSS uses.