code: private static int scanCaptureTypeSignature(String string, int start) {
  		// need a minimum 2 char
  		if (start >= string.length() - 1) {
  			throw new IllegalArgumentException();
  		}
  		char c = string.charAt(start);
  		if (c != C_CAPTURE) {
  			throw new IllegalArgumentException();
  		}
  		return scanTypeBoundSignature(string, start + 1);
  	}
docs: Scans the given string for a capture of a wildcard type signature starting at the given
  index and returns the index of the last character.
  <pre>
  CaptureTypeSignature:
  <b>!</b> TypeBoundSignature
  </pre>
  
  @param string the signature string
  @param start the 0-based character index of the first character
  @return the 0-based character index of the last character
  @exception IllegalArgumentException if this is not a capture type signature