"Pronto Hex IR Format" by none other than Barry Gordon. You can find this in User Documentation Subsection of the Classic Pronto Files Area.

I think there's also another document as well by Eugene (Eigeny) Eulanov that is a bit harder to read but also has some great info.

:-)

When I generated those codes, I did so using MakeHex and then when pulled into ProntoEditProNG for my TSU7000, the codes were shortened. The Classic Pronto FAQ and the NG FAQ have information on what the first 4 digits of the code mean as well. Link to FAQs can be found at the bottom of page in the respective forums.