too = plated_chunks.deepmerge(frm,too,_flags)
Merge the object, frm, into an object too. How values merge can be adjusted by _flags the same way _flags works in parsing chunks. same=merge is honoured here so some chunks can be appended rather than replace. We need to keep this separate as the act of merging will break how such things work.
This function is called recursively so as not to end up sharing values with any inputs.