Important Discovery: Vendor requests!

So who is a vendor?

I am guessing- in  my case - matlab is the vendor.  

What is a vendor request?

When matlab sends a code to USB, that code is passed to the USB call back function, which in turn will request what functions to run. 

How to write one?

For a Vendor requets to read bytes it should be

Direction IN / Req Type Vendor  / Target Device / Req Code your request code