Draining and filling coolant

[Ollymuk]

Hi all

Tomorrow my job is to drain the coolant and flush the heater matrix and refill the coolant.

The coolant.pdf on this site refers to both the "filler cap" and the "reservoir filler cap". I'm assuming the reservoir filler cap relates to the coolant tank on the nearside corner under the bonnet. If so, what does the "filler cap" refer to?

Olly

[Bob]

Cap on the radiator.