line height is straightforward enough, if you draw text with line height on N then you should move N pixels down for the next line.
Text baseline is the tricky part - if you want to e.g. put a taller piece of text next to a shorter one, then they should be put together so they share a baseline, but there's no decent way to get the text baseline.
The hack I use is to draw the text in a hidden span, and put a 1px inline-block span next to it, and check where the 1px span ends up. This works though it is ugly.
Text baseline is the tricky part - if you want to e.g. put a taller piece of text next to a shorter one, then they should be put together so they share a baseline, but there's no decent way to get the text baseline.
The hack I use is to draw the text in a hidden span, and put a 1px inline-block span next to it, and check where the 1px span ends up. This works though it is ugly.