To those wondering, as you know, form control variables are the names you have set for each field. Use those and treat as plain text. That way, you can format them however you like.
For me, I check “Output as HTML” and I can do:
Welcome [first_name],
and so on and so forth.
However, if you want to store a variable into a string like PHP or JS, you cannot do that as the parser is only for HTML.
