Accessing System Preference pane elements by Applescript

Question

I'm new to Applescript, and I'm trying to figure out how to set a hot corner in the Expose pane of System Preferences. I've been searching for Apple documentation, but I can't seem to find a good reference page.
Does anyone know what I'm doing wrong here?
<code>
tell application "System Events"
  tell process "System Preferences"
   tell menu bar 1
    tell menu "View"
     click menu item "Exposé & Spaces"
     delay 1
     tell tab group 1
      click radio button "Exposé"
      tell popupbutton
       tell menu 1
        click menu item "Spaces"
       end tell
      end tell
     end tell
    end tell
   end tell
  end tell
 end tell
</code>

Answer 1

I'll answer just three of your questions:
1. Is there a reason why we need to "end tell" "menu bar 1" after "click menu item 'Exposé & Spaces"' is done? (lines 4-11)
The reason is that the menu item "Start Screen Saver" is not part or the same hierarchy than the menu item "Exposé & Spaces". The menu item "Start Screen Saver" belongs to a menu which belongs to a pop up button which belongs to the group "Active Screen Corners" which belongs to a tab group which belongs to window "Exposé & Spaces" which belongs to the application "System Preferences".
2. What is the "window" in '*tell window "Exposé & Spaces"*'?
The window "Exposé & Spaces" is the window that replaces the "System Preferences" window when you click the menu item "Exposé & Spaces" of the "View" menu.
4. How come we need to "tell pop up button 1" before a click, instead of "click pop up button 1"?
Because we tell pop up button 1 to click AND tell menu 1 to do something. We could also have written:
tell group "Active Screen Corners"
click pop up button 1 -- or 2 or 3 or 4
tell menu 1 of pop up button 1
click menu item "Start Screen Saver" -- or any other menu item
end tell
end tell
As for your other questions, here are some references:
For GUI Scripting, have a look at this Web page:
http://www.macosxautomation.com/applescript/uiscripting/index.html
You should also download and use "UIElementInspector 1.3":
http://developer.apple.com/samplecode/UIElementInspector/
But before all, to get a better understanding of AppleScript, you should look at these pages:
http://www.macosxautomation.com/applescript/learn.html
http://developer.apple.com/documentation/AppleScript/Conceptual/AppleScriptLangG uide/introduction/ASLR_intro.html
(From my own point of view, AppleScript is rather difficult to learn, and GUI Scripting still more.)