Macro spec_mod 

macro_rules! spec_mod {
    (
        $(#[$SPEC_OUTER:meta])*
        Spec: (
            $SPEC_ID: ident,
            $SPEC_TITLE: expr,
            $SPEC_URI: expr
        );

        Subjects: [
            $(
                $(#[$SUB_OUTER:meta])*
                (
                    $SUB_ID: ident,
                    $SUB_URI: expr
                ),
            )+
        ];

        Requirements: [
            $(
                $(#[$REQ_OUTER:meta])*
                (
                    $REQ_ID: ident,
                    $REQ_URI: expr,
                    $REQ_LEVEL: expr,
                    [
                        $($REQ_SUB: expr,)*
                    ],
                    $REQ_STATEMENT: expr
                ),
            )+
        ];
    ) => { ... };
}

A macro for defining requirement