// main.mydsl
main XY {
    f1;
    f1;

    ref r1_1;     // reference to an element of the derived model
    ref r1_2;     // reference to an element of the derived model
}

// defined function library.mydsl
define function f1 {

    requirement r1 {

    }

}

main XY {
    requirement r1_1 {

    }

    requirement r1_2 {

    }

    ref r1_1;    // reference to an element of the derived model
    ref r1_2;    // reference to an element of the derived model
}

Requirement:
    {Requirement} 'requirement' identifier = ID '{'
        elements += ContentElement*
    '}'