http://www.authorize.net/support/AIM_guide_XML.pdf

While this guide is very verbose, I'm having a hard time knowing which field is a child of what. The table format doesn't really help much. An end tag is indicated simply by a bold line. The names are somewhat indented, but not by enough. The examples help somewhat, but not every field is included in the examples.

It would be helpful if all the end tags were included in the tables (name vs /name perhaps?), and with the names being indented, four spaces be tab woud be easier to read. More complete examples would also be helpful.

The table in "Minimum Required Elements" also is too similar to the other table. When doing a search, you can end up in either table. Perhaps in the main table do "<name>" and then in the Minimum table do "name". That way you can readily know which table you're in.

There also seems to be a descrepency. In createTransactionRequest it says "paymentType" in the table, but "payment" in the example. It seems "payment" is correct.