gistfile1.txt

 <global>
        <blocks>
            <lab_marcolini>
                <class>Lab_Marcolini_Block</class>
            </lab_marcolini>
            <core>
                <rewrite>
                    <messages>Lab_Marcolini_Block_Messages</messages>
                </rewrite>
            </core>
            </blocks>
            </global>