In section 22 of IEEE Std. 315, all electrical and electronic components (like transimission lines, waveguides, motors, resistors, etc.) are each given with their respective designators. Which in our case is not so convenient (since we mainly do PCB designs and of course we cannot put transmission lines on it, only connectors), so that's why we use the document Reference Designators.pdf from PCB Matrix. You can ask for this document in SupportNet. This document list all electronic components only, with their RefDes and it is more convenient since you don't have to browse anymore in the long list of components that you cand find in IEEE 315.