GridSuite has used the XML format [1] since the very beginning of its development.

Technically interested users can find some useful information on how to store Repertory Grids using the XML data format here =>  

GridXML.zip

Community: PCPTOOLS list on JISCMAIL

Fur further references see:
[1] Otto B. Walter, Andreas Bacher and Martin Fromm. A proposal for a common data exchange format for Repertory Grid data. Journal of Constructivist Psychology, 17:247-251, 2004.