I'm not sure if web pages display tooltips, as being discussed. there are some controls on some web pages that will do something such as open a menu or display information somewhere on a page if a mouse is hovered over the control. Most of the time, these don't matter enough to worry about. At times, they do and you may need a function like the JAWS mouse over function to work with that function of such controls.
But you may find that, by moving the mouse in NVDA over certain controls on certain web sites, you may hear something read as the screen changes. But NVDA doesn't identify such controls and it is not at all convenient to work with such controls if they display anything important. You don't know where the screen changed and you don't know if you've heard everything read. If you use the mouse over feature in JAWS, it tells you where the page changed, such as line 11. there is a jump to line feature in JAWS. Then you can jump back to where you were originally after you look at the area consisting of line 11 and anything below it that may have changed. This feature works with links. I don't know if any other controls function in this way. But in my experience, mouse over links seldom do anything important and the feature, though it is useful at times, is only useful a very small amount of the time. in other words, I generally don't worry about whether a page has such links or other controls. Though whether NVDA should have such a feature may be a good topic for discussion because even though rare, such a feature may allow you to do things on a page you can't otherwise.
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Definitely, it works quite consistently on the desktop and when
files/folders are selected. My main concern was specifically related to
web pages. Sorry for not emphasising it, I realise now I should have