What exactly is highlight roll-off, does HDR have it, and is it spelled roll off, roll-off or rolloff?

“In film photography, highlight roll off refers to the gradual transition from the highlights (the brightest parts of the image) to the shadows (the darkest parts of the image). This transition is not abrupt, but rather it occurs gradually, giving the image a smooth and natural-looking tonal range.” – Quora

“On film, if you were to overexpose an image severely, you would get a very soft and gentle gradient or rolloff that would take your image from it’s darkest point to it’s lightest. The brightest parts of the image would blend into the darker parts almost seamlessly, and the overexposed parts of your image would still be somewhat pleasing to the eye.” – Noam Kroll

“Almost all log gamma curves and the majority of raw recording formats don’t have a highlight roll-off. Any roll off that you might see is probably in the LUT’s that you are using. The whole point of log and raw is to capture as much information about the scene that you are shooing as you can. Log normally achieves this by recording every stop above middle grey with a constant amount of data, so even the very brightest stop has the same amount of recording data as the ones below it – there is no roll off.” – Alister Chapman

The way I understand it, highlight roll-off is when the brightest parts of the image transition into the clipped portions without abruptness. And for sure, HDR has zero highlight roll-off, which is why it is crucial to avoid clipping.