The ex/ vi specification is based on the historical practice found in the 4 BSD and System V implementations of ex and vi.
A restricted editor (both the historical red utility and modifications to ex) were considered and rejected for inclusion. Neither option provided the level of security that users might expect.
It is recognized that ex visual mode and related features would be difficult, if not impossible, to implement satisfactorily on a block-mode terminal, or a terminal without any form of cursor addressing; thus, it is not a mandatory requirement that such features should work on all terminals. It is the intention, however, that an ex implementation should provide the full set of capabilities on all terminals capable of supporting them.
A restricted editor (both the historical red utility and modifications to ex) were considered and rejected for inclusion. Neither option provided the level of security that users might expect.
It is recognized that ex visual mode and related features would be difficult, if not impossible, to implement satisfactorily on a block-mode terminal, or a terminal without any form of cursor addressing; thus, it is not a mandatory requirement that such features should work on all terminals. It is the intention, however, that an ex implementation should provide the full set of capabilities on all terminals capable of supporting them.