Players establishing facts about the world impromptu during play

[Emerikol]

Still not sure what this means!

Maybe I'm wrong but let me try to translate @pemerton. Feel free to correct me @pemerton if I get it wrong. He loves his fancy terms.

The rules as strictly written without any circumstantial adjudication by the GM. A tight control over GM interaction with the rules. Whereas D&D for example pretty much said the rules are optional and the DM is final authority in 1e.

 

[pemerton]

Purist for system is a particular approach to world/setting simulation: it relies on the system without needing stipulation/perturbation by "run time" input.

Still not sure what this means!

There is no need for the GM to inject complication or manage pacing: the system (eg encounter rules; resolution processes) will generate those "automatically". There is no need for the OSR-ish "rule of the Ming vase": the resolution process will generate those sorts of outcomes automatically (see eg the RM crit charts and skill charts). There is no need for ad hoc stipulation of NPC skills/abilities (the can there be skilled jewellers who aren't also skilled duellers? problem): the character generation process handles all this without trouble.

Everything about the fiction is yielded by the operation of the system mechanics.