Mermaid Railroad Diagram Cheat Sheet

A rule

A rule is a name, an equals sign and a definition, ending with a semicolon. terminal is a literal, nonterminal is another rule.

railroad-beta
    rule = sequence(terminal("a"), nonterminal("other")) ;
    other = terminal("b") ;

choice takes the alternatives in brackets. The rule cannot be called choice itself — that name is taken.

railroad-beta
    alt = choice(terminal("a"), terminal("b")) ;

optional wraps a part that may be left out.

railroad-beta
    rule = sequence(optional(nonterminal("tail")), terminal("head")) ;
    tail = terminal("t") ;

oneOrMore needs at least one, zeroOrMore needs none. Both wrap the part they repeat.

railroad-beta
    digits = oneOrMore(terminal("0")) ;
    words = zeroOrMore(terminal("x")) ;