@paltman This works great for display modes, but the "subdisplay" settings are not persisted in the URL.

"subdisplay" as referenced in scaife-viewer/frontend/#25 (and discussed in this comment on #26 pertains to any toolbar or selection options within a display mode.

So if I'm viewing a passage in "map mode" (/explore-homer/urn:cts:greekLit:tlg0012.tlg001.perseus-eng4:2.480?mode=named-entities), we should persist that I've chosen to view the map in parallel:

or in "alignments" mode, that I've selected the sentence level alignment:
/explore-homer/urn:cts:greekLit:tlg0012.tlg001.perseus-grc2:1.1-1.7?mode=alignments

Other examples I can think of off the top of my head (but double check each display mode component):

• "Folio Images" also has subdisplay state (for which columns are shown)
• "Syntax trees" (what is expanded / collapsed)

(And I'm open to introducing a better name than subdisplay if you have any ideas...maybe just calling it display mode state is clearer)

Looks good.

As noted in my comments above; there may be some patterns we want to establish in the future as part of shoring up the widget "contract" (what querystring params the widget expects / how it cleans up when destroyed, cataloging options in a constants module, etc).

@paltman love the encapsulation you added!

I think it also sets us up nicely if we need to further site-level overrides down the line (if we need to expose additional config, for example).