`Toggle` toggles all nested regions instead of only its own

[upsiflu]

Expected behavior: When I open or close the TOC, then the nested pages in other regions should remain visible.

Observed behavior: All nested pages (contingent) are affected.

[upsiflu]

update: as it stands, this only affects wrappers directly contingent under the toggle.

Workaround: insert one layer of wrapping.

I feel it's important to flesh out the semantics.

• Which patterns rely on toggle?
• For each of them, which behavior is more useful? Occlusions down the current region or the whole tree?
• If both behaviors are useful, then do we want escape hatches or an ostentative choice in the constructor such as { onlyAffectCurrentRegion : Bool }?
• How do related patterns operate? for example, Filter makes the search terms available to the whole nested tree. If we'd want to limit it to the current region, we'd need a way to map exactly that region down the tree (creating a context vertically nested and horizontally slim). Since the current implementation uses a function, a defunctionalized version is appreciated. -> new issue!
• How do the options bode with the main aim of less-ui, coherence over flexibility?

  Good: declarative, named state pattern at one locus. Ok: prefabricated stateful Ui snippets that are passed to functions elsewhere. Bad: manually intercepting the url.