Ok (preparing to cogitate whilst rolling a cigarette), DDE seems to relate to a lot of very specific things in a general way - my original query is all based from file extensions and exactly how Windows calls them during (shell) contextual invokations.
In a general sense as to "why" someone might use it (for those interested) it can be used to "silently" open and control an application - common examples relate to what/how the generic (on the surface) "Print" command you see populating shell menus works. (For instance whether Word or Notepad or OpenOffice is invoked for any particular document, when printing "invisibly" and how it's called.) Printing is actually the least it can do, but other examples get ridiculously complex for this post.
None too coincidentally I'm beginning to suspect this can also be related to x2's habit of opening
Help Links in IE vs FF. That thread was centred upon how windows defines its default browser, but I get the feeling it's in the core reference to the help-source itself, programmatically. (Nikos may sputter at this, but a recent investigation into "explorer replacement" and how x2 doesn't handle the Start Menu very well seems DDE related within the menu's application groups. I was just reading about this "somewhere" but I lost the link not thinking it important at the time, so details remain fuzzy. Much involves the interplay of a program and its document:
CALL ui.Interface.frontCall ("WINDDE","DDEExecute", [ program, document, command ], [result]), from
here.)
In any event, I did find definitions for the terms I was pursuing.
Forsooth, seeth
here as the following:
- Command: The value is the command line to start the associated application. "%1" is the file path to open. The application is usually the same for all the Verbs, but it need not be.
Ddeexec: The value is the default DDE Execute command string. It usually has an Application sub-key and a Topic sub-key. If there is no Ifexec sub-key, this string is used whether or not the application had to be started. If the Ifexec key is present, the Ddeexec command is used only if the application is already running.
Ifexec: The value is the DDE Execute string sent to the application just after it has been started. If this key is absent, the default Ddeexec value is sent instead.
Application: The DDE service name for the Shell to connect to for sending DDE Execute commands. This is frequently the same as the application name, for example "Excel" and "IExplore". Usually present if there are any DDE Execute strings for the Verb, if not Windows uses the executable name.
Topic: The DDE Topic name for the Shell to connect to for sending DDE Execute commands. Defaults to "System" if this key is absent.
So what of it for the common man? At first I was beginning to feel I was a morbid dog barking up a tree from hell - all "real world" examples I ran across involved using Excel to monitor stock-market issues real-time. (Like the Gods care anymore what those self-absorbed idiots do.) Interestingly, lots of details involve DDE packets of so-called "atoms" (which are strewn throughout the Windows cosmology - but that's another metaphor
.)
As fgagnon references in his link, these atoms revolve through the nucleus of 'Notifications' (WM_DDE_POKE, WM_DDE_EXECUTE, WM_DDE_DATA, WM_DDE_ADVISE, WM_DDE_UNADVISE, WM_DDE_INITIATE, and so on). These relate to DDE "aware" applications, as opposed to my focussing on shell menu commands.
Now I just feel I'm just a blithe little dog barking up a tree of fine-tuning minutiae.
In essence, the shell context applications mentioned in the first post are quite sufficient in their defaults for most modifications people would want to do. It's quite easy once you get the hang of it and well worth experimenting with.
However, as far as DDE is concerned for the real-world, the cigarette is burning... burning... gone.
* * *
fgagnon wrote:As an end user I'm not bored enough to delve into the details.
Fred, you know only too well what happens when I get bored. One of many of God's curses, and I utilise it to curse him right back,
as Caliban and Rimbaud would be my guides in hell. 
