In the documentation for H5LTget_attribute_info at <https://support.hdfgroup.org/HDF5/doc/HL/RM_H5LT.html#H5LTget_attribute_infothe documentation for the type_class argument is sadly lacking what is said is:
The class identifier. To a list of the HDF5 class types please refer to the Datatype Interface API help.
But the what I could find on the Datatype Interface API at https://support.hdfgroup.org/HDF5/doc1.6/UG/11_Datatypes.html does not give a clear answer. For example, I created an attribute using H5LTset_attribute_string. I would have expected the type_class for that to be H5T_STRING but H5T_STRING (in my fortran program) has a value of 216172782113784384 but type_class was set to 3 by H5LTget_attribute_info.