"This element should be used only to mark up writing which is topographically organized as a series of lines, horizontal or vertical. It should not be used to mark lines of verse (for which use l) nor to mark linebreaks within text which has been encoded using structural elements such as p (for which use lb)."
However, the only example given on the reference page happens to be a poem, which could be confusing for some reading that note. I recognise that it is not lines of verse that are being marked (but lines as they appear on a page), but it would be good to get another non-verse-related example on this reference page just to show that it doesn't matter what the intellectual interpretation of the text is, but how it is structured. Likewise, good to have one which gives individual coordinates on the lines.