<simpleType name="HeadShapeEnumType">
  <restriction base="string">
    <enumeration value="square">
      <annotation>
        <documentation>A square head, whose plan dimension headWidth is the length of one side. The most common cap form in rigid inclusion practice, since a square cap tessellates a square or rectangular column grid.</documentation>
      </annotation>
    </enumeration>
    <enumeration value="rectangular">
      <annotation>
        <documentation>A rectangular head, requiring both headWidth (the smaller plan dimension) and headLength (the larger). Used where the column grid spacing differs between the two horizontal axes.</documentation>
      </annotation>
    </enumeration>
    <enumeration value="circular">
      <annotation>
        <documentation>A circular head, whose plan dimension headWidth is the diameter. Typical where the cap is cast by enlarging the top of the column bore rather than formed separately.</documentation>
      </annotation>
    </enumeration>
    <enumeration value="hexagonal">
      <annotation>
        <documentation>A regular hexagonal head, whose plan dimension headWidth is the width across flats.</documentation>
      </annotation>
    </enumeration>
    <enumeration value="octagonal">
      <annotation>
        <documentation>A regular octagonal head, whose plan dimension headWidth is the width across flats.</documentation>
      </annotation>
    </enumeration>
  </restriction>
</simpleType>