node: markup | styles
markup: nodes
elements: "{" element* "}"
element: node | edge
node: (id (":" title)? nodes?) | edgenode
edge: idref arrow idref
arrow: ArrowLeft | ArrowRight | DiamondArrowLeft | DiamondArrowRight
ArrowLeft: "<--"
ArrowRight: "-->"
DiamondArrowLeft: "<>--"
DiamondArrowRight: "--<>"
id: text
title: string
string: """ text """


styles: style*
style: idref attributes? ":" style-elements
style-elements: "{" style-element "}"
style-element: key ":" value
key: text
value: text
idref: text
attributes: "(" attribute ")"
attribute: text ("," attribute)*