What are propellant ratios in part .cfg files for?

[Houdiny]

Hey! Beginner question here, I recently made my first custom part for ksp, an engine. While making the .cfg I noticed a field called "ratio" in the propellant section. Only answer I've found on google is from the documentation wiki which says it notes how much of a resource is used in 1s. Although, all engine .cfgs I've seen use 0.9 for the fuel and 1.1 for the oxidizer. So, what does that line do and how is it correlated to the overall workings of the part?

[wasml]

For the stock engines (0.9, 1.1) it's saying that for each 0.9 units of fuel used it will use 1.1 units of oxidizer. I'm guessing that behind the scenes KSP adds up the ratios and then divides by the total to make it easy on us.