Adjust leading with script

Since I’ve spent far to much time than is actually healthy working out why using 

myTypeRef.leading = 12;

just doesn’t work...

(On it’s own) - ya gotta turn out auto leading off at the same time!

So, for my future self and frustrated others I give you:
 

  // Add a new layer in the new document
  var artLayerRef = app.activeDocument.artLayers.add();

  // Specify that the layer is a text layer
  artLayerRef.kind = LayerKind.TEXT;

   //Get a reference to the text item so that we can add the text and format it a bit
  textItemRef = artLayerRef.textItem;

  textItemRef.contents = "Gwen Stefani is bananas!";
  textItemRef.size = 10;

  // Adjust the leading
  // Pour the lead, Ripley! Pour it!
  textItemRef.useAutoLeading = false;
  textItemRef.leading = 12;

To create text and give it a custom leading value.