Trying to make clothing in Blender 2.82.7 for PoserPro11 and can't set a constrain group that Poser will recognize. Can someone please give me a step by step on this? Been starting in Object Data properties, selecting the desired vertices. If someone can take from there I could figure what step I'm missing, Thank you!

What file format are you using to export the mesh from Blender to the other software? If you're using FBX, then according to the Blender docs, the result of using constraints is exported as a keyframe animation however the constraints themselves are not saved in the FBX. Also, if you are trying to export vertex groups, FBX format supports them, but Blender's FBX exporter does not write them yet either.

Edit to say: The Blender FBX exporter is lacking a lot of features that I've been accustomed to in some other packages I've noticed. At least when it comes to exporting geometry and animation. There is at least one addon I've heard which fixes some of the issues, but I can't recall what that addon is... or where to find it yet.

Edit: Ok, I found it. It's called "Better FBX Importer and Exporter" for Blender. It's available in the Blender Market, and it's not free. So I can't link directly from here.

I'm sorry if I wrote all of this for nothing. I still don't know what export option you use. haha.

Ok, I'm lost again. I switched to Blender from Silo 3D, where all I had to do was export the obj file from Silo and import to Poser. I didn't need any special software or addons to make the transfer. If I import something like a t-shirt or tunic that doesn't require a constrain group it works fine. I just can't make separate vertex groups that Poser recognizes.

Ok, so you're using OBJ? What blender does apparently try to map vertex groups to the "poly groups" . According to the Blender manual, Blender will write faces into OBJ groups based on the meshes vertex group. This does a "best guess", since a face’s vertices can be in multiple vertex groups. I'm not sure how Silo handled the same type of thing, but if you are using Blender 2.83, there is an option in there to export OBJ with Polygroups.

Click on the carrot triangle next to "Geometry" in the export dialogue box (on the right hand side). You will see a bunch of options with check boxes. One of them is "Polygroups". Check mark that option. It is not checked by default.

Here's a screencap of the export dialogue. Check the Polygroups option. Hopefully, that will do the trick. If not, then you'll probably have to assign them in the host app.

PS: As a side-note, I typically check the "Keep Vertex Order" on everything I export and import using OBJ unless it's special cases where I require split normals or creased edges.