The formal grammar of TAO is defined below in various notations.

Notes

1. All grammar definitions should be equivalent.

2. A reference implementation of the grammar is available as an interactive parser in JavaScript.

3. For brevity the following simple rules are defined only descriptively:

   • any is any printable Unicode character, as defined is YAML 1.2. specification.
   • any-except-meta is any excluding ` or [ or ]
   • linefeed is the line feed character (hexadecimal code 0x0A)
   • any-except-linefeed is any excluding the line feed character

Descriptive

• op is the symbol ` followed by any symbol.
• note is one or more symbols that are not ` or [ or ].
• tree is a tao inbetween a [ and a ].
• tao is zero or more parts each of which is a tree or an op or a note.

Augmented Backus-Naur Form (ABNF)

    op = "`" any
    note = 1*any-except-meta
    tree = "[" tao "]"
    tao  = *(tree / op / note)

Backus-Naur Form (BNF)

    <op> ::= "`" <any>
    <note> ::= <any-except-meta> | <note> <note>
    <tree> ::= "[" <tao> "]"
    <tao>  ::= "" | <tree> | <op> | <note> | <tao> <tao>