XML (eXtensible Markup Language) is a plain-text format for describing structured data. Although it can be written, read, and understood by people using simple tools, it's primary purpose is to allow software programs to exchange complex information in a reliable and unambiguous way.
The AASHTOWare Project™ Payroll XML Resource Kit should provide all the background information you need to produce valid Payroll XML files for use with AASHTOWare Project Civil Rights & Labor™ (formerly Trns•port CRLMS®). However, a deeper understanding of XML and XML Schema might be useful as well. The following links are to resources about XML and XML Schema in general. The links will take you away from the AASHTOWare Project Payroll XML Resource Kit, and are to sites not controlled by AASHTO or Info Tech, which are not responsible for their contents.