Re: Comma-seperated lists

Pete Resnick wrote:
> RFC 2822 not withstanding, were the following ever legal instantiations 
> of <#element>?
> 
> , element ,
> element, element,
> , , ,
> 
> 822 is not clear on this point to me, but it seems like those might be 
> allowed. My obs- lists currently don't allow them. Thoughts?



1.  Empty List

> Wherever this construct is used, null elements
>      are allowed, but do not  contribute  to  the  count  of  elements
>      present.   That  is,  "(element),,(element)"  is  permitted,  but
>      counts as only two elements.  Therefore, where at least one  ele-
>      ment  is required, at least one non-null element must be present.
>      Default values are 0 and infinity so that "#(element)" allows any
>      number,  including  zero;  "1#element" requires at least one; and
>      "1#2element" allows one or two.

I read the above as at least implying that an empty list that nonetheless 
contains commas is allowed.


2.  White Space Around Commas

> 3.4.2.  WHITE SPACE
> 
>         Note:  In structured field bodies, multiple linear space ASCII
>                characters  (namely  HTABs  and  SPACEs) are treated as
>                single spaces and may freely surround any  symbol. 

and

>      specials    =  "(" / ")" / "<" / ">" / "@"  ; Must be in quoted-
>                  /  "," / ";" / ":" / "\" / <">  ;  string, to use
>                  /  "." / "[" / "]"              ;  within a word.

I read this combination as rather explicitly allowing white space around a comma.


I'll note that all of this matches what I would have expected -- and even 
wished that 822 had been more clear about.

The goal with the lexical model and rule for white space was to allow its use 
to be extremely free.  If there was anywhere it might get used, without the 
ability to do parsing, the goal was to permit it.

d/
-- 

   Dave Crocker
   Brandenburg InternetWorking
   bbiw.net