trend

<xs:attribute name="trend" default="additive">
  <xs:simpleType>
    <xs:restriction base="xs:NMTOKEN">
      <xs:enumeration value="additive"/>
      <xs:enumeration value="damped_additive"/>
      <xs:enumeration value="multiplicative"/>
      <xs:enumeration value="damped_multiplicative"/>
      <xs:enumeration value="polynomial_exponential"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>