How can I create a skydome in Gazebo?

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I am trying to create a Gazebo world that contains an HDR (High Dynamic Range) skydome and a texture-mapped ground plane. The ground plane was easy, but I haven't discovered how to create the skydome. In Electric, empty.world in gazebo_worlds contains this:

<rendering:ogre>
<ambient>0.5 0.5 0.5 0.5</ambient>
<sky>
  <material>Gazebo/CloudySky</material>
</sky>
<grid>false</grid>
<maxUpdateRate>10.</maxUpdateRate>
<shadowTechnique>none</shadowTechnique>
<shadows>false</shadows>

</rendering:ogre>

I know how to replace Gazebo/CloudySky with a custom material that has a different texture map, but I don't know what texture map format <sky> expects. Examples are fish-eye, polar, vertical face map, etc. I haven't found any documentation describing how Gazebo skies work. Does anyone know of any? Can anyone point me to example world files that use skydomes? Lastly, does Gazebo support 16-bit float (i.e. half) OpenEXR files?