xmltangle is part of a system of Literate Programming. Literate Programming is a programming style in which the programmer writes an essay about his program which contains the program in its entirety. He then can either typeset his essay (known as weaving), or build the code (known as tangling). The tangle program allows the user to write their code in the way that it's easiest to think of and describe rather than how the compiler expects it. The tangle program can be instructed how to piece together your program properly.

xmltangle uses processing instructions to handle the tangling. That way, your documentation can be written using any XML DTD (actually, it doesn't even need a DTD). You can typeset your essay using the standard XML stylesheet methods, such as CSS, XSLT, or DSSSL. This program handles the tangling.