-If given, it contains an ARRAYREF for each different class type (i.e. one
-ARRAYREF if the data is only of one class type). These ARRAYREFS are the header
-fields which are an array of columns. In this case the first lines are not used
-as a header. Empty header fields will be ignored in objects.
+If given, it contains an ARRAY of the header fields for not multiplexed data.
+Or an ARRAYREF for each different class type for multiplexed data. These
+ARRAYREFS are the header fields which are an array of columns. In this case
+the first lines are not used as a header. Empty header fields will be ignored
+in objects.