then i still don't get it. When a simple line break would break a horizontal baseline-aligned grid, wouldn't it break a horizontal baseline-plus-some-space-aligned grid?

Although the css prop. "line-heigt" is not implemented in a convenient way, it is still deterministic as I understand from the quoted article:

"This is determ­ined by work­ing out the dif­fer­ence between the line-height and the font-size, divid­ing by 2, and then pla­cing the cal­cu­lated amount of space above and below each line of text."