MLTE renders text into a single rectangular frame. You can choose to have your application create arbitrarily wide lines or break lines at a certain width. If you choose to break lines, MLTE uses ATSUI line-breaking algorithms to control where a line breaks. Text is flowed into a visual line as long as it fits, then a new line is started with the first unbreakable unit (such as a word) that did not fit completely in the line.
If your application turns off ATSUI (this is not recommended), MLTE uses QuickDraw line-breaking algorithms. In this case, in scripts that use space characters to separate words, one (and only one) space character at the logical end of the text flowed into a visual line is consumed by the line break--it is ignored for measurements and not displayed.