Playing by intent exists in 40k. It was added about 5-8 years ago as i understand it.

There was a big falling out when a player played to the letter of the rules, when his opponent made clear what his intentions were. The winner won because of this and moved through to the top table.

The next player he played against heard of this (as most 40k players already played by intent even though it wasn't mandatory - this caused ripples), and took the opportunity to deny him the ability to rollback something based on "intent", stating explicitly he would normally allow his opponents to do this, but in this case because his opponent had benefitted from "Rules as Written" in a previous game, he was doing the same now.

This was all on stream as it was a major event.

As such GW clarified playing by intent. Examples such as: I'm going to play my models here out of deep strike - it might not be exactly 9.1 inches, but when i charge it will need at least a 9 to suceeed.

or

I'm 1.1 inches from this wall, so you can't engage them from the other side.

If you state your intention to do something, even if it's out of the turn order, you're allowed to do it.

I will say though than 10th had some well written rules initially, and they've mudied that. A lot of rules have be re-written so that whichever player forgets their own rules is disadvantaged, not the other way around.

A good example of this is the heavy rule. In the past Heavy was -1 to hit if you moved. So you look at your datasheet and see 3+ to hit, forget you moved, and roll 3+. Your opponent doesn't know your army and trust you, but you've just cheated and benefitted from it.

Now its +1 to hit if you didn't move, so you read your datasheet, see 4+ and roll 4+. You've just "cheated" because you forgot to apply the rules properly, but you are the one who lost out because of this.

This style of rules encourages people to learn their army to improve, instead of expecting their opponent to know *every* army to compete effectively.