Schematron using XPath 2.0 The attribute disp:Display_Direction/disp:horizontal_display_direction must be equal to one of the following values 'Left to Right', 'Right to Left'. The attribute disp:Display_Direction/disp:vertical_display_direction must be equal to one of the following values 'Bottom to Top', 'Top to Bottom'. The horizontal display axis () in display direction must match the name of an axis in the referenced Array () The vertical display axis () in display direction must match the name of an axis in the referenced Array () Display Dictionary: In the pds:Local_Internal_Reference class, the value of the pds:local_identifier_reference must match the value of the pds:local_identifer of an Array class or sub-class within the File_Area. Display_Dictionary: For Local_Internal_Reference in disp:Display_Settings, local_reference_type must equal 'display_settings_to_array'. The attribute disp:loop_flag must be equal to one of the following values 'true', 'false'. The attribute disp:loop_back_and_forth_flag must be equal to one of the following values 'true', 'false'. The attribute @unit must be equal to one of the following values 'frames/s'. The attribute @unit must be equal to one of the following values 'day', 'hr', 'julian day', 'microseconds', 'min', 'ms', 'ns', 's', 'yr'.