Function for extracting images from html source. through the html code supplied by add_html() and find any file that ends in one of the extensions defined in $obj->image_types.
Builds the multipart message from the list ($this->_parts). array of parameters that shape the building of the message. $params['html_encoding'] - The type of encoding to use on html. "7bit", "quoted-printable" or "base64" (all without quotes).