I want to have a background for each post, and that background is the first picture of the post. I had tried the following but it did not work:
<Variable name="body.background" description="BackGround" type="background" color='transparent' default="$(color)
url(<data:post.firstImageUrl/>) no-repeat fixed top center"
value="$(color) url(<data:post.firstImageUrl/>) no-repeat fixed top center"/>