[dssslist] 1) 'the principal port'; 2) port selection?

[Sean Champ <gimbal@xxxxxxxxxxxxxxxx>]

Hello,

I've some questions, myself, regarding 'ports'. 

I hope you'll pardon if I skip any start-of-page exposition. 

I have two questions:


** 1) "the principal port" (of what?)

In section 12.6.28.2 of the DSSSL standard [1] : regarding the
"multi-modes" property of the multi-mode flow object  class, it says:

   The specification of a port is either #f specifying the principal
   port or a symbol specifying a named port.  


Now, I understand the notion of /a/ principal port - generally, as
removed from any particular flow object. When the standard says /the/ 
principal port, though - I'm not meaning to pick at the standard,
here, honestly, but just to check at my understanding of it - it does 
mean /the principal port of the flow-object being created/ --  yah? 

(So, here, "the principal port" could  mean: the principal port of the
multimode flow-object being created .. ?)  



** 2) finding a a "principal port", or a named port, of an arbitrary
   flow object

(continuing on the text of the prior)

...Still, I do not understand what it /means/, outside of the basic
wording and the terminology.  I would appreciate any help, here.



Here is some of what I do understand, regarding the principal port:


 - In the 'multi-modes' property of a multi-mode flow-object (that
   property's value being - I presume - some manner of a list), there
   must exist exist a "principal port" specifier. 

 - The principal port may be made to contain things.


...and that's about all that I understand of it, honestly.



So, I guess that my main question would be:

  How would one go about, for pushing a flow object into  the
  principal port of an (arbitrary) multi-mode flow-object X?



Like, for example, if I want to add a 'box' flow-object into the
principal port (or any named port) of a 'multi-mode' flow object,
somewhere off in the blue ...

I suppose I could try something like the following, for at least
creating a box:

 (make box ; or however it would be said
  <stuff goes here>))

...but how could I manage to push the "value" of that box into the
desired "port" of the desired multi-mode flow object?

(How would I even "find" the principal port - or a named port - if
I'd been given the multi-mode flow object, directly ? - like, if the
selected flow-object had been stored as the value of a "local" variable.) 




Thank you


-- 
sean



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Footnotes: 
[1]  I think I've heard that it is a draft standard  - the one 'freely'
     available online, is the standard that I meant to refer to.