[Groff] Re: what is `.if v' for?

[Werner LEMBERG]

> Is it guaranteed that groff/troff will not let the user define a new
> alphabetic conditional (like t,n,e,o,v) that is true?  (It looks
> like any alpha that groff doesn't know about will be treated as
> false.)

New alphabetic conditionals are not allowed, causing a warning:

 file aaa:

    .ie a .tm true
    .el   .tm false

  # groff -ww aaa  

  aaa:1: warning: missing closing delimiter
  false

> Everything else (like using a num register or a string) can be
> broken by the user.  One would have thought the converter could
> posit a suitable device name for the \*(.T string, but it turns out
> that \*(.T can be changed by the user (why is this allowed?).

Both UNIX troff and GNU troff don't implement read-only string
registers.

BTW, `.if v' is really to identify -Tversatec on some troff variants.
Make a google search with the keywords `vroff troff' and you'll find a
lot of code fragments which use it.



    Werner