APOC load xls occasionally returns "$myKey" - what is that?

Experimenting with apocalyptic.load.xls on a complex sheet. At times I get (as part of the list value) something designated as $myKey:
" [".......", "I, S", "X", "X", "X", "I, S", "X", "X", null , "X", "X", "", "WITH {name: 'Anne'} AS a RETURN a[$myKey] AS res", null , ....."
What is the significance of this? I suspect that in the example above it is a manual line break that hides in the cell in the spreadsheet.
I would much prefer to skip such unprintable characters?