You can read the official press release and feature highlights for eDP 1.4a on VESA eDP 1.4b on DisplayPort.org Technical Archives:
The final production version that refined protocols to lower system costs and improve interoperability. Key Technical Features edp 1.4 specification pdf
Why does this matter?
Without this PDF, designing a compliant motherboard or display driver IC (DDIC) is virtually impossible. You can read the official press release and