Schematical sketch of an active margin
<ul><li><a href="//commons.wikimedia.org/wiki/File:Active_Margin.svg" title="File:Active Margin.svg">Active_Margin.svg</a>: <a href="https://en.wikipedia.org/wiki/User:Booyabazooka" class="extiw" title="en:User:Booyabazooka">en:User:Booyabazooka</a></li>
<li>derivative work: <a href="//commons.wikimedia.org/wiki/User:Luis_Fern%C3%A1ndez_Garc%C3%ADa" title="User:Luis Fernández García">LP</a> (<a href="//commons.wikimedia.org/wiki/User_talk:Luis_Fern%C3%A1ndez_Garc%C3%ADa" title="User talk:Luis Fernández García"><span class="signature-talk">talk</span></a>)</li></ul>
<ul><li><a href="//commons.wikimedia.org/wiki/File:Active_Margin.svg" title="File:Active Margin.svg">Active_Margin.svg</a></li></ul>