Ejs use the label for your element to define variable name for the created code.
So please use old standard name convention (beginning with an alphabetic character. and containing letters or numbers only.)
If you define a label as f(x) for a TextField. EJS will generate something like
The java will interprete f(x) as a function need to be called (instead of variable name).
That is why it produce error message when compiling the code.