...
XData Contents [ XMLNamespace = "http://www.intersystems.com/zen" ]
{
  <page xmlns="http://www.intersystems.com/zen" title="">
    <button id="btn1" caption="Тест" onclick="zenPage.Test();" />
    <textarea id="ta1" value="test"/>
  </page>
}

Method Test() [ ZenMethod ]
{
  d %page.%SetValueById("ta1","строка1"_$c( 13 , 10 )_"строка2")
  ; или так d %page.%SetValueById("ta1","строка1"_$$$EOL_"строка2")
  q
...
}