The Render.Msg.MarkupMsg type is need for synchronization of the source and rendered
text when using the Codemirror editor.
type MarkupMsg = SendMeta ({ begin : Basics.Int, end : Basics.Int, index : Basics.Int, id : String })
| SendLineNumber ({ begin : Basics.Int, end : Basics.Int })
| SelectId String
| HighlightId String
| GetPublicDocument Handling String
| GetPublicDocumentFromAuthor Handling String String
| GetDocumentWithSlug Handling String
| ProposeSolution SolutionState