There are two ways to communicate comments in DDEX messages. Either in the
<Comments> tag in the messages or using the XML's native commentary syntax
<!-- … -->. Neither of these approaches are recommended to be used as such commentary is targeted at a human reader – and DDEX messages are intended to be read and processed by computers. In any automated processing such comments would be disregarded.
If, however, comments are to be included (e.g. to help later retrieval in cases of audits or as part of a legal discovery process) XML's native commentary syntax
<!-- … --> is preferred.