source

<xsd:attribute name="source" type="xsd:IDREF" use="required">
  <xsd:annotation>
    <xsd:documentation>
      <p>The source attribute can refer:
        <ul>
          <li>either to the id of a glyph,</li>
          <li>or to the id of a port on a glyph.</li>
        </ul>
      </p>
    </xsd:documentation>
  </xsd:annotation>
</xsd:attribute>