In Arduino UNO R3 official schematic the AREF pin is not connected to anything:
While in most online Arduino schematics (such as this one) it's connected to a 100nf capacitor and then to the ground, the other two differences are a 100nf capacitor between VCC pin 7 and GND pin 8 and a 10uH inductor between AVCC and 5V.
Why in some schematics it's recommended to connect AREF to a 100nf capacitor?
Why there's a capacitor between pin 7 and 8?
Whats the use of that inductor on pin 20?