It all boils down to the wording of the bylaws for Nottingham Express Transit, which define the platform as the entire width of island platforms and (if I remember correctly) two metres from the edge of a single platform.
The bylaw allow Ticket Inspectors to issue penalty fares to unticketed passengers on the tram or on the platform, but specifically excludes people who have arrived on the platform other than by tram.
So the notices are put up on the platform merely for the administrative convenience of NET allow them to continue issuing a PFN if the tram stops and the challenged passenger gets off.
NET don't seem to care that these notices completely undermine the stance of other rail operators, who would claim in court that a "compulsory ticket area" should mean precisely that.
It really irritates me that the drafters of the bylaws were so lazy that they couldn't find a form of words that avoided this nonsense.
I have made a point of walking down the tram tracks at Royal Centre tramstop, as there is not other way through without passing along a "Compulsory Ticket Area" Platform; and making trams wait for me while I do so.
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Here you go. Not sure if these are the current version:
EDIT:
DEFINITIONS
“Compulsory Ticket Area” means
(i) Any tram; or
(ii) Where a tramstop has an island platform between two lines of the Authorised Tramway, that part of the tramstop lying between each of the platform edges facing those lines; and
(iii) At any tramstop with a platform that is not an island
platform; that part of the tramstop lying between, on one
side the platform edge facing a line of the authorised
tramway that is approximately 310 millimeters higher
than the nearer rail providing support and guidance for a
tram and, on the opposite side, for a distance equal to
and directly opposite that platform edge the greater of a
line 2 metres perpendicularly offset from the platform
edge and a line between platform demarcation markers
as defined in the Conditions of Carriage.
"In each case on which a notice is displayed which states that
the tram or area indicated in the notice is a Compulsory Ticket
Area;"
BYLAW 20
(4) No person at a tramstop compulsory ticket area shall be in breach of this Byelaw 20 unless he came there by alighting from a tram