Microsoft.Protocols.TestSuites.Common.RFC822AddressParser.InitialRegex C# (CSharp) Method

        private static void InitialRegex()
        {
            string qtext = @"[^" + RFC822AddressParser.Escape +
                RFC822AddressParser.NonAscii +
                RFC822AddressParser.CRLF + "\"]";
            string dtext = @"[^" + RFC822AddressParser.Escape +
                RFC822AddressParser.NonAscii +
                RFC822AddressParser.CRLF +
                RFC822AddressParser.OpenBr +
                RFC822AddressParser.CloseBr + "\"]";

            string quoted_pair = " " + RFC822AddressParser.Escape + " [^" + RFC822AddressParser.NonAscii + "] ";
            string ctext = @" [^" + RFC822AddressParser.Escape +
                RFC822AddressParser.NonAscii +
                RFC822AddressParser.CRLF + "()] ";

            // Nested quoted pairs
            string cnested = string.Empty;
            cnested += RFC822AddressParser.OpenParen;
            cnested += ctext + "*";
            cnested += "(?:" + quoted_pair + " " + ctext + "*)*";
            cnested += RFC822AddressParser.CloseParen;

            // A comment
            string comment = string.Empty;
            comment += RFC822AddressParser.OpenParen;
            comment += ctext + "*";
            comment += "(?:";
            comment += "(?: " + quoted_pair + " | " + cnested + ")";
            comment += ctext + "*";
            comment += ")*";
            comment += RFC822AddressParser.CloseParen;

            // x is optional whitespace/comments
            string x = string.Empty;
            x += "[" + RFC822AddressParser.Space + RFC822AddressParser.Tab + "]*";
            x += "(?: " + comment + " [" + RFC822AddressParser.Space + RFC822AddressParser.Tab + "]* )*";

            // An email address atom
            string atom_char = @"[^(" + RFC822AddressParser.Space + ")<>\\@,;:\\\"." + RFC822AddressParser.Escape + RFC822AddressParser.OpenBr +
                RFC822AddressParser.CloseBr +
                RFC822AddressParser.Ctrl +
                RFC822AddressParser.NonAscii + "]";

            string atom = string.Empty;
            atom += atom_char + "+";
            atom += "(?!" + atom_char + ")";

            // Double quoted string, unrolled.
            string quoted_str = "(?'quotedstr'";
            quoted_str += "\\\"";
            quoted_str += qtext + " *";
            quoted_str += "(?: " + quoted_pair + qtext + " * )*";
            quoted_str += "\\\")";

            // A word is an atom or quoted string
            string word = string.Empty;
            word += "(?:";
            word += atom;
            word += "|";
            word += quoted_str;
            word += ")";

            // A domain-ref is just an atom
            string domain_ref = atom;

            // A domain-literal is like a quoted string, but [...] instead of "..."
            string domain_lit = string.Empty;
            domain_lit += RFC822AddressParser.OpenBr;
            domain_lit += "(?: " + dtext + " | " + quoted_pair + " )*";
            domain_lit += RFC822AddressParser.CloseBr;

            // A sub-domain is a domain-ref or a domain-literal
            string sub_domain = string.Empty;
            sub_domain += "(?:";
            sub_domain += domain_ref;
            sub_domain += "|";
            sub_domain += domain_lit;
            sub_domain += ")";
            sub_domain += x;

            // A domain is a list of subdomains separated by dots
            string domain = "(?'domain'";
            domain += sub_domain;
            domain += "(:?";
            domain += RFC822AddressParser.Period + " " + x + " " + sub_domain;
            domain += ")*)";

            // A route. A bunch of "@ domain" separated by commas, followed by a colon.
            string route = string.Empty;
            route += "\\@ " + x + " " + domain;
            route += "(?: , " + x + " \\@ " + x + " " + domain + ")*";
            route += ":";
            route += x;

            // A local-part is a bunch of 'word' separated by periods
            string local_part = "(?'localpart'";
            local_part += word + " " + x;
            local_part += "(?:";
            local_part += RFC822AddressParser.Period + " " + x + " " + word + " " + x;
            local_part += ")*)";

            // An addr-spec is local@domain
            string addr_spec = local_part + " \\@ " + x + " " + domain;

            // A route-addr is <route? addr-spec>
            string route_addr = string.Empty;
            route_addr += "< " + x;
            route_addr += "(?: " + route + " )?";
            route_addr += addr_spec;
            route_addr += ">";

            // A phrase
            string phrase_ctrl = @"\000-\010\012-\037";

            // Like atom-char, but without listing space, and uses phrase_ctrl. Since the class is negated, this matches the same as atom-char plus space and tab
            string phrase_char = "[^()<>\\@,;:\\\"." + RFC822AddressParser.Escape +
                RFC822AddressParser.OpenBr +
                RFC822AddressParser.CloseBr +
                RFC822AddressParser.NonAscii +
                phrase_ctrl + "]";

            string phrase = string.Empty;
            phrase += word;
            phrase += phrase_char;
            phrase += "(?:";
            phrase += "(?: " + comment + " | " + quoted_str + " )";
            phrase += phrase_char + " *";
            phrase += ")*";

            // A mailbox is an addr_spec or a phrase/route_addr
            string mailbox = string.Empty;
            mailbox += x;
            mailbox += "(?'mailbox'";
            mailbox += addr_spec;
            mailbox += "|";
            mailbox += phrase + " " + route_addr;
            mailbox += ")";

            RFC822AddressParser.addreg = new Regex(mailbox, RegexOptions.Compiled | RegexOptions.IgnorePatternWhitespace);
        }
    }