hr - AP's lines seem intended to separate text blocks that have run into each other
underline - AP has deliberately giving emphasis to words or phrases - often accompanied by italic lettering though not always
--> Add to explanation of markup
related to #1134
See, for example, hr on: 157r, 157v (partial hr across the text which look like underlined words but mean to separate text blocks - these used to be underlines, now changed to hr) underline on: 86r (middle of text block with italic script), 169r (lists)