attrDefaults method provides access to a
attrData-class object's default attribute list. The
default attribute list of a attrData-class object defines what
attributes can be customized for individual data elements by
defining attribute names and default values.
attrDefaults(self, attr)
attrDefaults(self, attr) <- valueattrData-class instancecharacter vector of length 1 giving the name of
an attribute. Can be missing.attr is missing.