A drone operations hub is writing an algorithm to validate the callsigns of commercial drones registering for flight space (for example, "DRONE7").

variable.length returns the number of characters in variable.
variable.lower returns the characters in variable in lower case.

    valid = false

    while (valid == false)

        callsign = input("Enter callsign: ")

        if (callsign.length >= 5) AND (callsign.length <= 12)

            registeredCallsign = callsign.lower

            valid = true

            print("Callsign registered")

        else

            print("Invalid callsign format")

        endif

    endwhile

The algorithm needs testing to ensure the decision block (if-else statement) behaves correctly.