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


styles: "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)*