element echo {
        element metadata {
          element title {text} &                                 <!--could also be named attribute instead of element-->
          element author {text} &                                <!--as these elements have no children -->
          element subject {text} &
          element description {text} &
          element publisher {text} &
          element date {text} &                                  <!--Interleave connector, because the order is not -->
          element type {text} &                                  <!--important. Some quantifiers (*, ?, +) might be added.-->
          element format {text} &
          element identifier {text} &
          element source {text} &
          element language {text} &
          element relation {text} &
          element coverage {text} &
          element rights {text} 
            }
        element body {
          element front {
            element div {text}
            }?,
          element body {
            element div {text}*
            },
          element back {
            element div {text}
            }?
          }
}