This bug has been fixed in CVS. You can grab a snapshot of the
CVS version at http://snaps.php.net/. In case this was a documentation 
problem, the fix will show up soon at http://www.php.net/manual/.
In case this was a PHP.net website problem, the change will show
up on the PHP.net site and on the mirror sites.
Thank you for the report, and for helping us make PHP better.

Just a quick note, because the docs haven't shown up on
the site yet, and I don't have time to resync my phpdoc
tree - the zcontext is for specifying tuning parameters
and callbacks.  I did post an example to php-dev a while
back.
I will properly document this stuff when my workload
decreases to something just below fever pitch.

Still open, I'll document it.

This has been briefly documented, I lack the knowledge to take it further.  Here's some related information:

 Re: [PHP-DEV] streams and options
  http://marc.theaimsgroup.com/?l=php-dev&m=101922976301407
Also, in NEWS:


  PHP now has a new stream system that allows it to 
  do some clever stuff with fopen() and fsockopen().  
  As a result:
  . URL wrappers natively supports https:// URLs
  . fsockopen() adds support for ssl:// and tls://
    connections via TCP/IP
  . copy($srcfilename, $destfilename) can now be used with 
    URL wrappers
  . zlib wrappers/streams can be used even on systems
    without fopencookie()
  . Added 'compress.bzip2://' stream and wrapper support.
  . Added user-space streams - it is now possible to define 
    a class in PHP code and register it as a URL wrapper.
  . Most extensions now support streams when passing files, 
    which means that those extensions will support URL
    wrappers. (Wez)

More related php-dev threads:

 Stream Filters and Interfaces (a bit long)
  http://marc.theaimsgroup.com/?l=php-dev&m=101924701219677
 
 URLs, fopen wrappers and RFC 2718
  http://marc.theaimsgroup.com/?l=php-dev&m=101915071800583

Am unassigning from self, remains open.

whoa, kudos for the footwork, philip! :)

I still don't have time to properly document this, but I'm
pasting part of my email conversation with Philip here,
just in case someone else does get the time before I do.
Thanks very much to Philip for the effort in researching
this stuff!

Wez said:
> The concept is this:
> Sometimes it is useful to specify some more advanced tuning paramters
> for a file (or stream) before it is opened.  In the case of HTTP,
> it is also useful to be able to share context settings - the main
> thing here is to store cookies from one request and then use them
> for subsequent fopen("http://...") requests.
> 
> This concept was expanded to allow callbacks to monitor progress:
> you should be able to find more details on this on the marc archives -
> search for something like "stream progress notification"; this was
> implemented in response to someone requesting the feature for FTP,
> so adding FTP in there might help narrow the search.
> 
> The context functions were (re)named as follows:
> 
> stream_context_create()
> stream_context_get_options()
> stream_context_set_option()
> stream_context_set_params()
> 
> Context parameters have the following structure, much like an
> array, so I'll display it like an array:
> 
> context => array(
>    notification => callback for notification function
>    options => array(
>        http =>  array(optionname => optionvalue) // for http 
>        ftp => ftp wrapper options
>        ... => other wrapper options
>    )
> )
> 
> ATM, only the notification parameter has been set and no options
> for the other wrappers have been finalized, so it only makes sense
> to document that part of it right now.

And Philip said:
Feel free to add the information below to the bug 
report, I unassigned myself, and wrote all the 
information I knew into it.  See:

  http://bugs.php.net/bug.php?id=17784

Btw, that thread you speak of (stream progress 
notification" is here:

  RFC: stream notification handlers
  http://marc.theaimsgroup.com/?l=php-dev&m=101826854819192

Somehow I missed it.  Hopefully if you mention the 
stuff below in that report someone will document it.
Sorry I can't :(  Btw, this is some cool stuff!  I'm 
slowly understanding it.

Thank you for your bug report. This issue has already been fixed
in the latest released version of PHP, which you can download at 
http://www.php.net/downloads.php

Still not documented (not sure why Ilia closed it - perhaps
by mistake).

With a little (lot) of help from Wez, I'll document this.

Didn't know this bug was here till Philip asked me to document contexts..... fortunately I had just done it anyway :)

I love it when a plan comes together.