regex引擎位于何处?

We're covering sed in class and I was wondering about the way sed uses the regex engine. Does each program (sed, awk, grep, etc.) use a regex engine that was programmed into it, or is there a regex engine tool/library/function that the individuals developing sed, grep, etc. just implement in their code? Is the engine built into the OS and then called by the tools utilizing it? I feel like knowing this will help me understand the level of standardization regex has achieved. Who made you, regex engine? Where is your source code?We're covering sed in class and I was wondering