Set position of window with AppleScript

Question

I'm trying to set the position of the Messages.app chat window using AppleScript.

tell application "System Events"
    set position of window 1 of application "Messages" to {100, 100}
end tell

With this code I get an error:

error "Messages got an error: Can’t set «class posn» of window 1 to {100, 100}." 
number -10006 from «class posn» of window 1

What does that mean?

If I try the same code with Finder it works. But most of the other applications don't work.

Answer 1

I found a solution. Setting the bounds of the window works. I have no idea why using the position doesn't work.

tell application "System Events"
    set friendBounds to {4289, 400, 4479, 1600}
    set chatBounds to {3583, 400, 4289, 1599}
    set bounds of window "Buddies" of application "Messages" to friendBounds
    set bounds of window "Messages" of application "Messages" to chatBounds
end tell

Answer 2

tell application "System Events"
    set position of first window of application process "Messages" to {100, 100}
end tell  

Enable Access for assistive devices to run this script.

Answer 3

As of writing, the other solutions did not work for me on macOS 10.14 Mojave. I managed to find this solution:

tell application "System Events" to tell process "Safari"
    set position of window 1 to {0, 50}
    set size of window 1 to {600, 650}
end tell