Comment "preview"... doesn't.
Comments on extensions have a "preview" feature, which is handy, but of limited practical value because the preview version of the user's comment is formatted completely differently from how the comment will actually be displayed when published.
The comment preview is shown in the body-text font size, at the full page width, and has newlines preserved. But when comments are actually posted, they're shown in a smaller font and narrow width, and newlines are stripped out so the entire text is run together.
The preview would be more useful if it applied the same styling.