Jumbo90 is a library written in Fortran for creating CML documents. Actually, Jumbo allows you to create XML, CML and STMML (another markup language closely related to CML). After a moments thought you may ask why do we need a library to write things? I mean, you can always type
Well, while in theory it is a fairly simply task to write CML, or indeed any XML, in any language, in practice it's not quite that easy. Balancing tags that are opened at one end of a 2000 line source file and closed at the other or even opened and closed in different source files, is an unnecessary memory exercise, and balancing them in the right order a pain. More importantly, you'll probably only spot your mistake when you try to process the file, and given that XML is case sensitive it's a pretty easy to make a mistake. Furthermore, CML elements will often be built up in a standard manner using a large number of tags - and it can be fairly tedious typing in all of these. Add to this the fact that it is extremely difficult to correctly indent an XML document whose structure is as dynamic as that of the underlying program  (just using write statements). So, we decided that it was probably worth our while to create a library for handling the more tedious or tricky elements of creating a CML document. We also added functionality to check the well-formedness of all XML. In fact, most programming languages provide utilties for performing these seemingly simple tasks
The original idea for Jumbo90 came from Peter Murray-Rust, who has a similar but much more rounded suite of tools written in Java, called Jumbo. I then converted Peter's original F77 code into F90, but it suffered a little from its F77 inheritance, so now the base XML formatting layer of Jumbo is provided by Alberto Garcia's WXML library.
The Jumbo90 README containing a breakdown of all Jumbo90 subroutines is available here
Jon Wakelin, March 2004
 It's only a cosmetic feature but it's very useful when you need someone to read the file, of course, there's nothing wrong with writing a 12M XML file in a single line.