Joe, the reason why your method is not good enough is that the usual ABC software absolutely requires those coloned things (X:, T:, etc., not the actual notes) directly at the beginning of the line. We would like to copy-and-paste from Mudcat into our ABC editors (I use ABCExplorer) - it does not work with those space characters. Is that different with the software you are using?

Mudcat does not actually misinterpret the <pre> tag, but it takes the liberty to add a space after each <br> tag it inserts. This "phenomenon" has been known for a long time.

In other words: whoever wants ABC text with aligned columns, must use <code> and  . I learned that trick from another poster about two years ago, and it did not seem new then.