title: In UI service how to get the content of a RichTextArea?
body: <p>Class RichTextArea has no setName() so I'm wondering how to use its content in a Handler function.
  the <a href="https://developers.google.com/apps-script/class_richtextarea?hl=fr-FR" rel="nofollow">doc</a> refers to the Google Web Toolkit but I can't get how to make that work in GAS.
  Thx</p>