Apparently refers to WD23-WIP1 http://www.oasis-open.org/apps/org/workgroup/energyinterop/download.php/42101/energyinterop-1-0-spec-wd23-wip1.pdf
Sections 5.4 and 5.5 refer to VEN and VTN that are interchangeable in their service interactions. If instead the references are to Parties then the discussion would apply to both VEN/VTN interactions and the transactive interactions.
NOTE SECTIONS 5.5 and 5.6 in wd24.