Formula to show or hide element

Please, what is the meaning of the formula $if(gv(xx)=1,f,r)$ and $if(gv(xx)=1,f,a)$?
Is it different of $if(gv(xx)=1,1,0)$ or $if(gv(xx)=1,always,never)$?

The only one i understand is $if(gv(xx)=1,always,never)$

The formula is used generally in the “visibility” parameter which accepts “always” and “never” as an option. The others might be used in different context, every preference in Kustom can be turned into a formula so other preferences (like opacity for example) could take a number between 0 and 1 so in that case you would use $if(gv(xx)=1,1,0)$

Hope it helps

Thanks any way, but I am interested to learn the formula with the letters r and f, I saw it in a template to switch visibility, but maybe it has another function.