Expression editors should contain on-hover tooltips

The current expression editor is very basic and does not contain any method to view function signatures/docs. Normally, you would expect to be able to hover over a function to see how to use it, or hold something like ctrl and right click to open docs on that function.

Instead you only get a vague message if you have an error.

This tells me nothing about what each string should be. Which one is the text to search for, which is the string to replace with, what's the last value? The expected behavior would be like is seen below, as this is an extremely common pattern for most IDE's: