title: Can't set settable accessibility attribute in AppleScript
body: <p>After reading the question “<a href="https://stackoverflow.com/questions/10487350/programmatically-select-text-range-in-textedit" title="Programmatically select text range in TextEdit">Programmatically select text range in TextEdit</a>”, I am curious why the <em>AXSelectedTextRange</em> attribute can’t be set in AppleScript even though the properties indicate it is settable.</p>
  
  <p>Open a TextEdit document, type a few lines, highlight a portion and run the script below to test.</p>
  
  <pre><code>activate application "TextEdit"
  tell application "System Events"
      set attr to attribute "AXSelectedTextRange" of text area 1 of scroll area 1 of window "Untitled" of application process "TextEdit"
      attr's properties -- determine if settable
      set attr's value to {1, 2}
      delay 1
      attr's value
  end tell
  </code></pre>
  
  <p>Is there something different about how AppleScript handles accessibility attributes  that I am misssing?</p>