custom-theme/choose_doc_version.html

<select class="form-control" onchange="if (this.value) window.location.href=this.value">
  <option value="/latest">
    Version: master
  </option>
  <option value="/v1_12_0/" {% if config.extra.version=="v1_12_0" %}selected="selected" {% endif %}>
    Version: 1.12.0
  </option>
  <option value="/v1_11_0/" {% if config.extra.version=="v1_11_0" %}selected="selected" {% endif %}>
    Version: 1.11.0
  </option>
  <option value="/v1_10_0/" {% if config.extra.version=="v1_10_0" %}selected="selected" {% endif %}>
    Version: 1.10.0
  </option>
  <option value="/v1_9_0/" {% if config.extra.version=="v1_9_0" %}selected="selected" {% endif %}>
    Version: 1.9.0
  </option>
    <option value="/v1_8_0/" {% if config.extra.version=="v1_8_0" %}selected="selected" {% endif %}>
    Version: 1.8.0
  </option>
  <option value="/v1_7_0/" {% if config.extra.version=="v1_7_0" %}selected="selected" {% endif %}>
    Version: 1.7.0
  </option>
  <option value="/v1_6_0/" {% if config.extra.version=="v1_6_0" %}selected="selected" {% endif %}>
    Version: 1.6.0
  </option>
  <option value="/v1_5_0/" {% if config.extra.version=="v1_5_0" %}selected="selected" {% endif %}>
    Version: 1.5.0
  </option>
  <option value="/v1_4_0/" {% if config.extra.version=="v1_4_0" %}selected="selected" {% endif %}>
    Version: 1.4.0
  </option>
  <option value="/v1_3_0/os/introduction" {% if config.extra.version=="v1_3_0" %}selected="selected" {% endif %}>
    Version: 1.3.0
  </option>
  <option value="/v1_2_0/os/introduction" {% if config.extra.version=="v1_2_0" %}selected="selected" {% endif %}>
    Version: 1.2.0
  </option>
  <option value="/v1_1_0/os/introduction" {% if config.extra.version=="v1_1_0" %}selected="selected" {% endif %}>
    Version: 1.1.0
  </option>
  <option value="/v1_0_0/os/introduction" {% if config.extra.version=="v1_0_0" %}selected="selected" {% endif %}>
    Version: 1.0.0
  </option>
  <option value="/v0_9_0/os/introduction" {% if config.extra.version=="v0_9_0" %}selected="selected" {% endif %}>
    Version: 0.9.0
  </option>
</select>