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higherClassification (http://rs.tdwg.org/dwc/terms/higherClassification)

@return [String]
A list (concatenated and separated) of taxon names terminating at the
rank immediately superior to the taxon referenced in the taxon
record. This is used to fit the entire higher classification for a taxon
into a single field. Recommended best practice is to order the list
starting with the highest rank and separating the names for each rank
with a semi-colon (";").

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