The answer to the question appears to be in comment 13; the width of the newline character is used at one point but then assumed to be the same as the width of

The answer to the question appears to be in comment 13; the width of the newline character is used at one point but then assumed to be the same as the width of a space later on: > I think I see. There's a block at the bottom of RenderText::computePreferredLogicalWidths() which is only hit if wordLen == 0 and !isNewline (which is the case here) which measures the width of the one character at index i and adds it to currMaxWidth. In our situation, that's the leading newline character. > Then, later, we subtract it out like this: "widths.max -= font.width(RenderBlock::constructTextRun(&space, 1, style));". This expects that the width of this initial character is equal to the width of a space.