While looking for a solution for infopath offline support, I came by the
DataInterop sample in the SDK (http://msdn.microsoft.com/library/en-
us/ipsdk/html/ipsdkRetrievingCreatingRecordsDataInt_HV01082955.asp?
frame=true#). Looking at the JS code in the form, it looked like it's
pretty straight forward. The sample has a group OfflineData in the main
data source that is supposed to cache the secondary data source when going
offline. What worried me right away is that this node is just a group, with
no fields inside, unlike the actual secondary datasource. However I stuck
with their solution, and after some customization for my own prototype, I
got the infamous exception "Element [long thing for dfs]:myFields is
unexpected accordint to the content model of parent element [long thing for
my]:nameOfMySecondaryDataSource" when attempting to go cache the secondary
DOM. This exception occurs on the following line:
objOfflineDataNode.parentNode.replaceChild(objNewOfflineDataNode,
objOfflineDataNode);

This problem has risen a few times on this forum, yet no solution has been
expressed. I have never even tested out the SDK, assuming what they post
there will work. However it is beyond me how they replace a node that
appears just as a group with nothing inside in the main connection with a
group that has tons of stuff inside in the secondary data source.