JSON5 grammar expressed in EBNF form. 

PS: I don't know what is appropriate syntax highlighter for this, so I'm using "modula2" because why not. I also inserted <ZWSP> after backslash to preserve syntax highlighting, this character has nothing to do with actual JSON5 syntax and should be ignored.

```modula2
json5_text = expression_with_whitespace

expression_with_whitespace = [white_space] , expression , [white_space]

expression = literal
           | array_literal
           | object_literal

literal = null_literal
        | boolean_literal
        | signed_numeric_literal
        | string_literal

null_literal = 'null'

boolean_literal = 'true'
                | 'false'

(* Source Characters *)

source_character = .
                (* any Unicode code unit *)

line_terminator = <LF>
                | <CR>
                | <LS>
                | <PS>

line_terminator_sequence = <LF>
                         | <CR>
                         | <LS>
                         | <PS>
                         | <CR> , <LF>

white_space = white_space_element
            | white_space , white_space_element

white_space_element = white_space_character
                    | comment

white_space_character = <TAB>
                      | <VT>
                      | <FF>
                      | <SP>
                      | <NBSP>
                      | <BOM>
                      | <USP>

comment = multi_line_comment
        | single_line_comment

multi_line_comment = '/*' , [multi_line_comment_chars] , '*/'

multi_line_comment_chars = (source_character - '*') , [multi_line_comment_chars]
                         | '*' , [post_asterisk_comment_chars]

post_asterisk_comment_chars = (source_character - ('*' | '/')) , [multi_line_comment_chars]
                            | '*' , [post_asterisk_comment_chars]

single_line_comment = '//' , [single_line_comment_chars]

single_line_comment_chars = single_line_comment_char , single_line_comment_chars

single_line_comment_char = source_character - line_terminator

(* Character classes *)

decimal_digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9'

non_zero_digit = decimal_digit - '0'

hex_digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' | 'a'
          | 'b' | 'c' | 'd' | 'e' | 'f' | 'A' | 'B' | 'C' | 'D' | 'E' | 'F'

ascii_letter = ascii_letter_lowercase
             | ascii_letter_uppercase

ascii_letter_lowercase = 'a' | 'b' | 'c' | 'd' | 'e' | 'f' | 'g' | 'h' | 'i' 
                       | 'j' | 'k' | 'l' | 'm' | 'n' | 'o' | 'p' | 'q' | 'r'
                       | 's' | 't' | 'u' | 'v' | 'w' | 'x' | 'y' | 'z'

ascii_letter_uppercase = 'A' | 'B' | 'C' | 'D' | 'E' | 'F' | 'G' | 'H' | 'I' 
                       | 'J' | 'K' | 'L' | 'M' | 'N' | 'O' | 'P' | 'Q' | 'R'
                       | 'S' | 'T' | 'U' | 'V' | 'W' | 'X' | 'Y' | 'Z'

(* Numeric Literals *)

signed_numeric_literal = '-' , numeric_literal
                       | '+' , numeric_literal
                       | numeric_literal

numeric_literal = decimal_literal
                | hex_integer_literal
                | non_finite_literal

non_finite_literal = 'Infinity'
                   | 'NaN'

decimal_literal = decimal_integer_literal , '.' , [decimal_digits] , [exponent_part]
                | '.' , decimal_digits , [exponent_part]
                | decimal_integer_literal , [exponent_part]

decimal_integer_literal = '0'
                        | non_zero_digit , [decimal_digits]

decimal_digits = decimal_digit
               | decimal_digits , decimal_digit

exponent_part = exponent_indicator , signed_integer

exponent_indicator = 'e' | 'E'

signed_integer = decimal_digits
               | '+' , decimal_digits
               | '-' , decimal_digits

hex_integer_literal = '0x' , hex_digit
                    | '0X' , hex_digit
                    | hex_integer_literal , hex_digit

(* String Literals *)

string_literal = '"' , [double_string_characters] , '"'
               | "'" , [single_string_characters] , "'"

double_string_characters = double_string_character , [double_string_characters]

single_string_characters = single_string_character , [single_string_characters]

double_string_character = source_character - ('"' | '\​' | line_terminator)
                        | '\​' , escape_sequence
                        | line_continuation

single_string_character = source_character - ("'" | '\​' | line_terminator)
                        | '\​' , escape_sequence
                        | line_continuation

line_continuation = '\​' , line_terminator_sequence

escape_sequence = character_escape_sequence
                | '0'
                | hex_escape_sequence
                | unicode_escape_sequence

character_escape_sequence = single_escape_character
                          | non_escape_character

single_escape_character = '"' | "'" | '\​' | 'b' | 'f' | 'n' | 'r' | 't' | 'v'

non_escape_character = source_character - (escape_character | line_terminator)

escape_character = single_escape_character
                 | decimal_digit
                 | 'x'
                 | 'u'

hex_escape_sequence = 'x' , hex_digit , hex_digit

unicode_escape_sequence = 'u' , hex_digit , hex_digit , hex_digit , hex_digit

(* Array Literals *)

array_literal = '[' , [white_space] , ']'
              | '[' , [white_space] , element_list , ']'
              | '[' , [white_space] , element_list , ',' , [white_space] , ']'

element_list = expression , [white_space]
             | element_list , ',' , [white_space] , expression , [white_space]

(* Object Literals *)

object_literal = '{' , [white_space] , '}'
               | '{' , [white_space] , property_name_and_value_list , '}'
               | '{' , [white_space] , property_name_and_value_list , ',' , '}'

property_name_and_value_list = property_assignment , [white_space]
                             | property_name_and_value_list , [white_space] , ',' , [white_space] , property_assignment , [white_space]

property_assignment = property_name , [white_space] , ':' , [white_space] , expression

property_name = identifier_name
              | string_literal
              | numeric_literal

identifier_name = identifier_start
                | identifier_name , identifier_part

identifier_start = unicode_letter
                 | '$'
                 | '_'
                 | '\​' , unicode_escape_sequence

identifier_part = identifier_start
                | unicode_combining_mark
                | unicode_digit
                | unicode_connector_punctuation
                | <ZWNJ>
                | <ZWJ>

unicode_letter = ascii_letter
              (* + any character in the Unicode categories "Uppercase letter (Lu)", "Lowercase letter (Ll)", "Titlecase letter (Lt)", "Modifier letter (Lm)", "Other letter (Lo)", or "Letter number (Nl)" *)

unicode_combining_mark =
                      (* + any character in the Unicode categories "Non-spacing mark (Mn)" or "Combining spacing mark (Mc)" *)

unicode_digit = decimal_digit
             (* + any character in the Unicode category "Decimal number (Nd)" *)

unicode_connector_punctuation =
                             (* + any character in the Unicode category "Connector punctuation (Pc)" *)


```