[pstricks] Meaning of @beginspecial, @endspecial and @setspecial

[Christoph Bersch]

Hi,

what is the meaning or purpose of the @beginspecial and @endspecial 
procedures in PSTricks?
I noticed, that variables defined within
@beginspecial ... @endspecial cannot be accessed in Postscript code. 
Some code, however, is not enclosed by those procedures. That is the 
reason why the following gives a Postscript error (bad code, only for 
demonstration!):

\psline(!/asdf 3 def 0 0)(3, 3)
\psline(2,1)(! 5 asdf)

whereas

\pnode(!/asdf 3 def 0 0){A}
\psline(2,1)(! 5 asdf)

work.

What controls if the code is encapsulated in the @...special procedures 
and what is there purpose?


Thank you,
Christoph