A store over a web storage the host hands it (the page's localStorage,
or anything with the same three members), one JSON entry per instrument
under prefix. A text that does not parse throws from get, which the
helper reports and treats as no drawings.
A store over a web storage the host hands it (the page's
localStorage, or anything with the same three members), one JSON entry per instrument underprefix. A text that does not parse throws fromget, which the helper reports and treats as no drawings.