> the layout might change if for example the spacing is calculated based on the vh unit (or vmax in portrait mode, or vmin in landscape mode).
That sounds like a good thing, and pretty much the entire point of using viewport-relative units?
I'd certainly expect vh/vw-based layouts to change when I change the size of my viewport, whether by hiding and showing ancillary UI elements (e.g. sidebars or control bars of my browsers) or by manipulating the browser window directly.
Most of the time, yes. But the layout might jump just because you scroll up/down a little. For example, the spacings might get slightly larger when you scroll down and slightly smaller when you scroll up.
That sounds like a good thing, and pretty much the entire point of using viewport-relative units?
I'd certainly expect vh/vw-based layouts to change when I change the size of my viewport, whether by hiding and showing ancillary UI elements (e.g. sidebars or control bars of my browsers) or by manipulating the browser window directly.