When typing any function (like "contains" in this example) in an expression you need to know the signature of the function. If you don't know it by heart, you will have to go to the documentation by pressing the questionmark-button and than searching for the function.
This idea: show the function's signature as soon as you typed the function's name.
Like many other IDE's do.
This has slowed me down a lot sometimes, constantly having to double check parameters. Why is there no “cheat sheet” or link for functions on the expressions window? Seems like that should have been there at least; can’t be that hard to at least link to existing documentation. Hopefully the parameter details will be shown in the auto-complete window as well soon. I see this has been sitting here for a year now. Don’t hold my breath I guess...