Currently if renderWorldCopies = false and the viewport is not square, the map does not allow the user to zoom out enough to show the entire map.

You can see this in the render world copies example by fully zooming out and toggling the option:

Zooming out is limited to when the map's bounds are reached on the left and right sides (with a wide viewport) or the top and bottom sides (with a tall viewport). I assume this is the intended behavior. Edit: This appears to not be the intended behavior; see comment below.

However, this can be abrupt for users who expect to be able to see the entire map when they attempt to fully zoom out the map.

I would like an option to allow the map to be "underzoomed" until the entire map is visible when renderWorldCopies = false, whereby the background area outside the map is transparent or assigned a color:

Perhaps the option could be something like showEntireMap or allowUnderZoom, though I'm not familiar with best practices in naming and implementation.

(One could think of this as (un)constraining the zoom and pan of the map, which the OpenSeadragon image viewer does nicely here: https://openseadragon.github.io/examples/ui-zoom-and-pan/.)