radio on till door opens

These questions actually pertain to a car with a negative door trigger but i thought i'd post here to keep things cleaner. anyways: As per the diagram here: https://www.the12volt.com/relays/page5.asp#drto under "Radio on until door opened" There is something i dont understand. Please note, i'm sure that this works but i just wanted to clear some confusion i had. On the left Relay here are my questions: 1.) I see that 87 and 86 are both connected to Radio accesory, does this mean just directly to the stereo's acc wire? No connection is made to the vehicles acc? 2.) If so, when the car is off or on for that matter, doesn't that mean that 86 is not being powered by anything at all? Maybe i don't know what the ACC wire on a stereo is supposed to be used for, but i thought that when the stereo gets +12v on the ACC line, it knows to power the stereo. (and when it loses it, to turn it off) right? 3.) if 86 is not being powered and 85 is just ground, then that means that the relay is NOT energized therefore 30 and 87a have continuity, doesn't this make the relay useless? Since 30 is just going to give +12v to 87a which is connected to nothing. The only way i can understand this relay making any sense is if the RADIO GAVE +12V on the ACC line instead of receiving it. Please correct me if i'm wrong here.

Is it dangerous doing the first way? I have only 2 relays right now but i'll go get another if the second one is a lot better. could u please explain why the second method is better?

So what does the relay set up do. I have a 07 mustang, and my radio stays on until a door is open, which is kinda cool. Does this set up turn the radio off when the key is removed or what?

actually, i'm trying to get my car to be like yours. I have an 06 mazda3 that i want to have my stereo keep playing until i open my door with the key out of the barrel. I wanted to add a timer function on this as well just in case but no idea how to. Any suggestions?

I am actually trying to get the hang of relays and how they work and just looked at this sample yesterday. Here is what I got: Relay 2 on the right has pin 87a being ground when the coil isn’t charged. 87a is connected to one side of the coil on relay 1 so with the car off, relay 1 pin 85 is at ground. When the vehicle turns on the accessory wire gets 12V which powers relay one (completes the coil circuit as 85 is ground). With relay one energized the constant 12v on pin 30 of relay 1 connects to pin 87 of relay 1 which is also the accessory wire. Relay 2 is still not energized at this time.. The person turns the vehicle off but since the constant 12V is now connected to the accessory wire through the relay the radio stays on… When the door gets opened a ground gets sent to pin 85 of relay 2 energizing relay 2. This REMOVES ground from 87a which is how relay 1 is getting energized thus removing the constant 12V from the accessory wire.. When the door is then closed the coil on relay 2 is not energized anymore which puts 87a back to ground but since the accessory wire has lost its constant 12v relay 1 will not be repowered until the vehicle is started again.. That is my uneducated explanation..