Some defined terms operate in a hierarchy - sometimes that is unwise.
Display Sub-System – comprising bus-stop information display electronics and communications Equipment fitted to Real-Time Passenger Information Display (RPID) structures.
The RPID is something that stands at bus stops and shows bus arrival and departure times.
(1) displayed minutes-to-arrival (DMA) and other service information displayed on all RPIDs;
This says all RPIDs, but means only the bus stop RPIDs meant in the particular section of the document.
5.7.2. On-Board RPID
5.7.2.1. An On-Board RPID shall display next stop information for travelling passengers.
An on-board RPID is on the bus ceiling behind the driver – it is nothing like the thing at a bus stop, and displays quite different information.
….
5.7.2.10. The RPID shall incorporate a fault monitoring function
This refers to the On-Board RPID only.
We will have to handle
5.2 The XYZ …..
......
5.8 The Specialised XYZ….
.......
5.8.3 The XYZ shall have …. – meaning the Specialised
XYZ
This is notionally the same as
John was holding a Glock. Fred knew the gun was loaded.
We have to handle use of class hierarchy and use of local context (which changes when the section ends).
The first case is more like
5.0 Lion
5.1 The lion chases gazelles….
6.0 Ant Lion
6.1 The lion seizes the ant….
They are two very different animals.
The effort required to work out which statements refer to which RPIDs and then remember the difference is wasteful.
The On-Board RPID should have been called an OPID or similar.