Keyboard method for opening the Mac's On-screen Keyboard

See this solution for Mac OS X 10.6.

On Mac OS X 10.5, you can open the following program:

/System/Library/Components/KeyboardViewer.component/Contents/SharedSupport/KeyboardViewerServer.app/Contents/MacOS/KeyboardViewerServer

At least in 10.7 and later you can just open the KeyboardViewer application:

open -a KeyboardViewer

It has a few drawbacks though:

• If you close the keyboard window by for example pressing the close button, the KeyboardViewer process stays running and keeps using something like 0-10% CPU.
• If you open KeyboardViewer again after that, it doesn't reopen the keyboard window.
• The keyboard window is made visible when I run scripts that emulate keystrokes or use Alfred's clipboard history.

All of those can be avoided by opening the keyboard window from the input menu:

tell application "System Events" to tell process "SystemUIServer"
    tell (menu bar item 1 where description is "text input") of menu bar 1
        click
        click (menu item 1 where title ends with "Keyboard Viewer") of menu 1
    end tell
end tell

A workaround for the second issue is to terminate KeyboardViewer if it is running but has no windows:

if application "KeyboardViewer" is running then
    tell application "System Events" to number of windows of process "KeyboardViewer"
    if result is 0 then
        quit application "KeyboardViewer"
        delay 0.1
        activate application "KeyboardViewer"
    else
        quit application "KeyboardViewer"
    end if
else
    activate application "KeyboardViewer"
end if