private String parseQuotedString() {
            StringBuilder result = new StringBuilder();
            expect('"');

            while (!eof()) {
                char next = peek();
                if (next == '"') {
                    break;
                }
                skip();

                // The backslash octet ("\") can be used as a single-octet quoting
                // mechanism within quoted-string and comment constructs.  Recipients
                // that process the value of a quoted-string MUST handle a quoted-pair
                // as if it were replaced by the octet following the backslash.
                if (next == '\\') {
                    if (eof()) {
                        throw syntax("Expected character after escape");
                    }
                    result.append(peek());
                    skip();
                } else {
                    result.append(next);
                }
            }

            expect('"');
            return result.toString();
        }
Gets the optional structured syntax suffix.

<p>For example given, "application/foo+json", this method returns
"json". Given "application/foo+baz+json", this method returns
"json". Given "application/json", this method returns an empty
{@code Optional}.

@return Returns the optional structured syntax suffix value with no "+".
smithy-utils/src/main/java/software/amazon/smithy/utils/MediaType.java