post processing - What, technically, is happening when one adjusts the 'Exposure' setting in a raw editor?

Since the photograph has already been taken by the time it is being edited, 'adjusting the exposure' of a RAW file must have a specific technical meaning (which I have struggled to find) Can someone explain that technical meaning?

Here are two possibilities:

'Adjusting the exposure' of a RAW file using a RAW editor is actually an intelligent editing function which approximates what the picture would have looked like if it had been taken at a different exposure. (If this is the case, how does it work? How does it differ to adjusting an image's brightness?)

OR

'Adjusting the exposure' of a RAW file using a RAW editor is a kind of filtering function that determines which information in the RAW file will be used to create the next version of the image? (If this is the case, how does it work, and what determines the initial settings before the 'exposure' is 'altered'?)