These options are chosen in the material properties dialog box. In the "outliner" window select a material > RMB > Edit Material > YafaRay Tab > Select the object type. When that material is applied to an object, that object takes on that mesh type, either Mesh, Volume, Meshlight, or Light Portal. See the "Meshlights" example file from my website for reference. The "Noise Volumetrics" example shows how a Volume object works.
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