How write .bnf to Intellij Idea

Question

I have this code structure:

STRING 1
// possible comment
{
Multi
line
text
}

STRING 2
...

And write this bnf:

{
    ...

    tokens = [
        t_lbrace = '{'
        t_rbrace = '}'
        t_string = "STRING"
        t_line_comment="regexp://.*"
        t_number='regexp:[1-9]\d*'
        t_whitespace = 'regexp:[^\S\r\n]'
        t_newline = 'regexp:\n|\r\n'
        t_block = 'regexp:\{[\s\S]*?}'
    ]
}

string_num ::= t_string t_whitespace* t_number t_whitespace* t_newline
block ::= t_block

How to properly organize the file structure?

I searched the Internet and did not find a single normal example of writing your own bnf structure.