_is_level_reference(self, key, axis=0)
To be considered a level reference, :None:None:`key` must be a string that:
(axis=0): Matches the name of an index level and does NOT match a column label.
(axis=1): Matches the name of a column level and does NOT match an index label.
Potential level name for the given axis
Axis that levels are associated with (0 for index, 1 for columns)
Test whether a key is a level reference for a given axis.
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