Hey there @transcoderm… that is a great question. The Wappler team may have a specific answer for you.
There are previous posts where we have debated the abilities of the graphical interface to create more complex formats and expressions, and there is a sense that there will be an “Expression Builder” type of interface coming some time in the future. Note the current window is called “Data Formats” and is therefore a formatting window rather than an expression builder. I know what you ask for is relatively simple, but things can often be much more complex as I am sure you have experienced.
For now, I have just learned the syntax and I type all these things in code, using the graphical tools to build some things that I can’t remember the syntax for.