code: private static void checkQuotedString(final String quotedString) {
  		boolean quotedPair=false;
  		for(int i=0;i<quotedString.length();i++) {
  			final char ch=quotedString.charAt(i);
  			if(quotedPair) {
  				checkArgument(QUOTED_PAIR.get(ch),"Invalid quoted-pair character '%s' in quoted string '%s' at %d",ch,quotedString ,i);
  				quotedPair=false;
  			} else if(ch==SLASH) {
  				quotedPair=true;
  			} else {
  				checkArgument(QDTEXT.get(ch),"Invalid character '%s' in quoted string '%s' at %d",ch,quotedString ,i);
  			}
  
  		}
  		checkArgument(!quotedPair,"Missing quoted-pair character in quoted string '%s' at %d",quotedString,quotedString.length());
  	}
docs: Checks the given quoted string for illegal characters, as defined in RFC
  7230, section 3.2.6.
  
  @throws IllegalArgumentException
  in case of illegal characters
  @see <a href="http://tools.ietf.org/html/rfc7230#section-3.2.6">Hypertext
  Transfer Protocol (HTTP/1.1): Message Syntax and Routing, Section
  3.2.6</a>