Creating a complex system in possession by simple individual instructions
Using Barça right now as hypothetical example.
1) "Rakitic, drop deeper or towards the side to open space. When Alves and Messi are wide, go forward centrally."
2) "Alves, don't give always width, but stay more central for circulation. Open space for Messi. When both Messi and Rakitic are more central, give width or stay back.
3) "Busquets, if there is space in front of you and two of the three players on the right of you are rather deep and/or wide, advance forward."
4) "Iniesta, if there is space on the right side of you and two of the three players on the right wing are rather deep and/or wide, move lateral to fill. If it's filled, stay half-left or drop."
5) "Suarez, move towards the right when Messi is more central and no one is giving width. Drop centrally, if the situation for a layoff after a vertical pass arises."
6) "Neymar, try to position yourself between CB and FB when Suarez is going towards the right side. Otherwise stay on the left and give width when the ball is on the right, when it comes to you look for dribbles. When Messi comes in from the right, go diagonally towards the goal."
7) "Alba, under- and overlap Neymar when the play is switched to him or give width near the 3rd line when he is more narrow. When Messi goes diagonally towards the goal from the right, run towards the 2nd post."
8) "Pique, move a bit more narrow towards the middle, when Alves stays deeper or Rakitic drops. When they don't, go wider and open space centrally for Busquets or even ter Stegen."
9) "Mascherano, support from half left, open space centrally for Busquets to drop when there is an oppositional high press. Look for passes towards Iniesta."
10) "Messi, do whatever you want."
This enables them to play at least 34 positional structures (though all over the pitch) based only on the interactions on the right side (Messi, Rakitic, Alves) and balancing movements.
Some of them can be created one from another within advancing the ball forward.
Two (or, rather, three to four) examples:
Might do an in-depth article about this. Might even include a bit about training methodics and sessions for it. Just an example to show how flexibility and complexity in possession can be created by simple instructions and easy understandable language for the players using a well-known team.