I have a large volume that I just want to render the nearest area of, not the areas farther away. I dialed "yon" down to about 15 on the camera, and preview shows just the area I wish to render, but once it starts going, I see everything is getting rendered. Other than cutting the model apart, is there a way to render just a specific range in front of the camera, using the hither/yon settings or some other method?

If there are only one or two material zones using the z component in the P node linked to transparency may be an option. If Superfly another approach would be to add a transparent plane and use lightinfo node to hide what's behind but this would also require all mats to be changed. Adding a plane geometry to block behind and then green screening is another thought (requires two renders). If interested in the first two options let me know and I'll post an example.

Sure, if you don't mind - the first method sounds interesting.

Does anyone know the purpose of the hither and yon settings, if not to constrain the render range?

Originally the hither and yon settings were meant just for Preview mode. They were not supposed to affect rendering.

I seem to recall hearing they were changing that with Superfly, and Superfly would take hither and yon "clipping planes" into account when rendering, but I don't know if they actually did it.

So below isn't quite working as expected, the offset is double what I expected but can't figure out what's going wrong. I thinking if you can place the model so the clip point is at z = 0 it should be enough to at least prove or not the idea works. The process involves adding these nodes to each of the materials to be clipped.

The "P" node generates the offset from the Z axis in inches with negative values going backwards. The idea with the "offset "node is to adjust the clip distance - for example "10" should mean to clip 10 inches further back but at the moment it seems to be doing double for some reason. The next node "Mask Minmum" forces any z value in front of the clip distance to zero (or off), The "Remove Sign" forces any non-zero input to be "1" (or "on") . This is then fed into a blender node to set transparency.

To my recollection a value of 1.0 in the p- node corresponds to 0.1 inch units, but I may be mistaken.

Yes, the posts I read had 1 Poser Unit = 8.6 feet and 1 pnode corresponds to 1 PU/1000. So 1 pnode unit = (8.6x12)/1000 = 0.1032 inches or to put it another way 10 pnode units ~ 1 inch.