org-export-filter-superscript-functions is a variable defined in `ox.el'.
Its value is
nil
This variable may be risky if used as a file-local variable.
Documentation:
List of functions applied to a transcoded superscript.
Each filter is called with three arguments: the transcoded data,
as a string, the back-end, as a symbol, and the communication
channel, as a plist. It must return a string or nil.