+x::="x"
// indentation styling...
// literal blocks [[need to ignore bracing]] double-colon style?
// definition -- by prior line indentation, like headings in the original structured text
//////////////////////////////////////////////////////////////////////////////
-s ::= {Doc} => top
+s ::= { Doc } => "top"
Doc ::= Header Body /ws => doc
Header ::= "header" { kv */ ws } /ws => header