static isNegativeWithBrackets(valueString, leftBracket, rightBracket) {
        return valueString.charAt(0) === leftBracket && this.contains(valueString, rightBracket);
    }
Return `true` if the very first character is the opening bracket, and if the rest of the `valueString` also has the closing bracket.

@param {string} valueString
@param {string} leftBracket
@param {string} rightBracket
@returns {boolean}