class

<xsd:attribute name="class" use="required">
  <xsd:annotation>
    <xsd:documentation>
      <p>The class attribute defines the semantic of the glyph, and influences:
        <ul>
          <li>the way that glyph should be rendered,</li>
          <li>the overall syntactic validity of the map.</li>
        </ul>
      </p>
      <p>The various classes encompass the following PD SBGN elements:
        <ul>
          <li>Entity Pool Nodes (EPN),</li>
          <li>Process Nodes (PN),</li>
          <li>Logic Operator Nodes,</li>
          <li>Sub-glyphs on Nodes (State Variable, Unit of Information),</li>
          <li>Sub-glyphs on Arcs (Stoichiometry Label),</li>
          <li>Other glyphs (Compartment, Submap, Tag, Terminal).</li>
        </ul>And the following ER SBGN elements
        <ul>
          <li>Entities (Entity, Outcome)</li>
          <li>Other (Annotation, Phenotype)</li>
          <li>Auxiliary on glyps (Existence, Location)</li>
          <li>Auxiliary on arcs (Cardinality)</li>
          <li>Delay operator</li>
          <li>implicit xor</li>
        </ul>
      </p>
    </xsd:documentation>
  </xsd:annotation>
  <xsd:simpleType>
    <xsd:restriction base="xsd:string">
      <!-- Entity Pool Node classes (PD only) -->
      <xsd:enumeration value="unspecified entity"/>
      <xsd:enumeration value="simple chemical"/>
      <xsd:enumeration value="macromolecule"/>
      <xsd:enumeration value="nucleic acid feature"/>
      <xsd:enumeration value="simple chemical multimer"/>
      <xsd:enumeration value="macromolecule multimer"/>
      <xsd:enumeration value="nucleic acid feature multimer"/>
      <xsd:enumeration value="complex"/>
      <xsd:enumeration value="complex multimer"/>
      <xsd:enumeration value="source and sink"/>
      <!-- Activities (AF) -->
      <!-- perturbation is deprecated in AF as Activity Node in milestone 3. -->
      <xsd:enumeration value="perturbation"/>
      <xsd:enumeration value="biological activity"/>
      <!-- Entities (both PD and ER) -->
      <xsd:enumeration value="perturbing agent"/>
      <!-- Other (PD only) -->
      <xsd:enumeration value="compartment"/>
      <xsd:enumeration value="submap"/>
      <xsd:enumeration value="tag"/>
      <xsd:enumeration value="terminal"/>
      <!-- Process Node classes (PD only) -->
      <xsd:enumeration value="process"/>
      <xsd:enumeration value="omitted process"/>
      <xsd:enumeration value="uncertain process"/>
      <xsd:enumeration value="association"/>
      <xsd:enumeration value="dissociation"/>
      <!-- PD, ER and AF -->
      <xsd:enumeration value="phenotype"/>
      <!-- Logical Operator classes (PD, ER and AF) -->
      <xsd:enumeration value="and"/>
      <xsd:enumeration value="or"/>
      <xsd:enumeration value="not"/>
      <!-- Subglyph on glyph classes (both PD and ER) -->
      <xsd:enumeration value="state variable"/>
      <xsd:enumeration value="unit of information"/>
      <!-- Entities classes (ER) -->
      <xsd:enumeration value="entity"/>
      <xsd:enumeration value="outcome"/>
      <!-- Other (ER) -->
      <xsd:enumeration value="interaction"/>
      <xsd:enumeration value="influence target"/>
      <xsd:enumeration value="annotation"/>
      <xsd:enumeration value="variable value"/>
      <xsd:enumeration value="implicit xor"/>
      <!-- Logical Operator classes (ER and AF) -->
      <xsd:enumeration value="delay"/>
      <!-- Auxiliary on glyph classes -->
      <xsd:enumeration value="existence"/>
      <xsd:enumeration value="location"/>
      <!-- Auxiliary on arc classes -->
      <xsd:enumeration value="cardinality"/>
      <!-- used for cis / trans and stoichiometry -->
      <!-- NB Arc classes are in a separate enumeration -->
      <!-- The use of observable is deprecated in newer versions of SBGN.
                                Because it occurs in older versions of the SBGN spec,
                                we will keep it around indefinitely.
                                !-->
      <xsd:enumeration value="observable"/>
    </xsd:restriction>
  </xsd:simpleType>
</xsd:attribute>