Inconsistent bottomLeft behavior

[Larry Snider]

I'm trying to anchor a card to the bottom left corner of the screen
but I want to dynamically determine the screen size, card size, etc
and then change it's location.

When doing something like this I sometimes get "coordinate is not a
point" errors at run time...but not all the time, mind you.  Putting
numbers in the coordinate position of bottomLeft works but not using a
variable.

on mouseDoubleUp
    put the working screenRects into tSCR
    --put item 4 of tSCR into tYHeight

    --put "0," & tYHeight into tVarLoc

    set the bottomLeft of this stack to 0,item 4 of tSCR
    --set the bottomLeft of this stack to tVarLoc

    put the decorations of this stack into tDecorations
    switch tDecorations
        case "title,minimize"
            set the decorations of this stack to empty
            break
        case empty
            set the decorations of this stack to "title,minimize"
            break
        default
            set the decorations of this stack to "title,minimize"
            break
    end switch
end mouseDoubleUp

Can anyone guide me on the proper way to snap a card to the edge of
the screen?  I'd like to add the option to choose which corner to
anchor to but if variables in the coordinates are sketchy I won't.
;-)

Thanks.

Larry