interface I{
    /** X */
    function bar();
}

trait T{
    /** Y */
    function bar(){}
}

class C implements I{
    use T; // EDIT: summary is resolved to Y & X. See an example below
}

-----------------------

interface I{
    /** X */
    function bar(stdClass $abc);
}

trait T{
    /** Y */
    function bar(){} // This will give an error
}

class C implements I{
    use T;
}