EBNF

Below we show the EBNF grammar:

Document         ::= Line*

Line             ::= CommentLine | NodeLine | IndentedTextLine

CommentLine      ::= IndentOpt? "#" TEXT? Newline

NodeLine         ::= IndentPrefix NodeHeader Separator? InlineValue? Newline

IndentedTextLine ::= IndentPrefix TEXT Newline

NodeHeader       ::= SpecialTextNode | NodeName Namespace?

SpecialTextNode  ::= ":" NodeName ":"       (* Indicates freeform text *)

NodeName         ::= Identifier

Namespace        ::= "(" Identifier ")"     (* e.g. (com.example.docs) *)

InlineValue      ::= TEXT                   (* Optional inline value *)

Separator        ::= ":"                    (* Colon separates key and value *)

IndentPrefix     ::= IndentOpt | NumericIndent

IndentOpt        ::= (TAB | SPACES4)*       (* Tabs or 4 spaces *)

NumericIndent    ::= Digit+ ":"             (* e.g., 2: for level 2 *)

Newline          ::= "\n" | "\r\n"

Identifier       ::= IdentifierChar ( IdentifierChar )*

IdentifierChar   ::= Letter | Digit | "_" | "-" | " "

Letter           ::= ? any Unicode letter ? (* A–Z, a–z, á, é, ñ, etc. *)

Digit            ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"

TEXT             ::= ? any printable character except newline ?