Sorry, I misread your question. Paul's solution will work for you.

-Lloyd

That is not possible via expressions. One workaround way to do it could be to have several layers and have the slider change the opacity of the layers to show and hide them.

-Lloyd

You can use my Throttle script to Purge and Turn Multiprocessing on and off from a dockable UI palette.

http://aescripts.com/throttle-n-purge/

-Lloyd

The app.executeCommand() is an unsupported function and is therefore not guaranteed to work in future versions. I would only use it when there is no other choice. Creating an adjustment layer is easy using supported api methods: var newAdjLayer = app.project.item(index).layers.addSolid(color, name, ...

I hate to say you are correct Nab. I already confirmed and filed the bug for Win7 CS5 although I was only experiencing it on scripts run as panels not on scripts run as windows (ie from the scripts menu or launched from ExtendScript Toolkit)

-Lloyd

I have never heard of such a script and it would be more complicated than you think to create. There would be a ton of considerations that would need to be handled. I would be a handy script though, just won't be easy to do.

-Lloyd

The scripting api gives you access to the command line so theoretically you could write a script that renders the individual passes out of ae then through the command line invoke another script written in python that assembles all the passes into a multi-channel exr. For example, in my Immigration s...

Crashed for me as well on Mac CS5

http://aescripts.com/trim-to-layer-above/

(Answered this on the cow but am cc'ing it here for completeness) Instead of using a try/catch you can use the canAddProperty() method: To check if you can apply an effect use the PropertyGroup canAddProperty() method (page 148 of the CS3 scripting guide): app.project.item(index).layer(index).proper...

It's not very straight forward, I would use the AVItem usedIn attribute on the parent comp, then on it's parent comp, etc.:

-Lloyd

Page 26 of the CS3 Scripting Guide:

Application open() method

app.open()
app.open(file)

Description
Opens a project.
Returns
A new Project object for the specified project, or null if the user cancels the Open dialog box.

If you want to pass an argument to your function you can do it like this:
-Lloyd