[SOLVED] Why does “Bluetooth Low Energy primer” document state that a BLE observer device needs a transmitter and may or may not have a receiver?

Why does “Bluetooth Low Energy primer” document state that a BLE observer device needs a transmitter and may or may not have a receiver?

I was reading the Bluetooth LE primer document and stumbled across the table given below:

My doubt is how can receiver be optional if the observer's only job is to receive BLE data and not transmit any thing back. Should it not be the other way? Transmitter being optional and Receiver being mandatory?

P.S. I understand that in hardware BLE radio implements both Tx and Rx and its left upto the application to use either or both.

I am just reading the BLE specification document and have not implemented anything yet however this observer device definition did not make sense to me. I expected observer to have a Rx mandatory and Tx optional.

Solution

I believe this is a mistake or a copy/paste error in the document. If you have a look in the official Bluetooth specification you'll find the correct description (Bluetooth Core Specification v5.3, Vol 3, Part C, Section 2.2.2.2):