((element "bikes" "-" "-" (zero-or-more "bike") "")
   (element "bike" "-" "-" "(frame, wheel+, brake*, lock*)" "")
   (element "frame" "-" "-" "EMPTY" "")
   (element "wheel" "-" "-" "EMPTY" "")
   (element "brake" "-" "-" "EMPTY" "")
   (element "lock" "-" "-" "EMPTY" "")
   (attribute "bikes" ())
   (attribute
      "bike"
      (("kind" ("mountain-bike, racer-bike, tourist-bike, other") "tourist-bike")))
   (attribute "frame" (("frame-number" "CDATA" "#REQUIRED")))
   (attribute
      "wheel"
      (("size" "CDATA" "#REQUIRED") ("tube-kind" "CDATA" "#IMPLIED")))
   (attribute
      "brake"
      (("kind" "CDATA" "#IMPLIED") ("brand" "CDATA" "#IMPLIED")))
   (attribute
      "lock"
      (("brand" "CDATA" "#IMPLIED")
         ("insurance-approved" ("true" "false") "#REQUIRED")))
   (entity "Number" "CDATA")
   (entity "Boolean" "(true | false)"))