Note that while the FIX Session Protocol is based upon "Tag=Value" syntax for the Standard Header, Standard Trailer, and the Administrative Messages which make up the FIX Session Protocol, it is possible to send FIXML or other XML-based content ("payload") via the FIX Session Protocol. The FIXML or other XML-based content is enclosed in a traditional "Tag=Value" FIX standard header via the standard header's XmlDataLen <212> and XmlData <213> fields and followed by the "Tag=Value" FIX standard trailer. This allows a FIX Engine (software which implements the FIX Session Protocol) to transmit FIXML or other XML-based content via the robust, real-time asynchronous transport which has been in use for many years. The generic MsgType <35> field value of "n" (lowercase n) for "XML message (e.g. non-FIX MsgType)" can be used when transmitting XML content which is not defined with a FIX MsgType <35>.