a bit mor documentation (#789)

src/main/java/org/htmlunit/attachment/AttachmentHandler.java

@@ -83,7 +83,7 @@ default boolean handleAttachment(final WebResponse response, final String attach
     default boolean isAttachment(final WebResponse response) {
         final String disp = response.getResponseHeaderValue(HttpHeader.CONTENT_DISPOSITION);
         if (disp == null) {
-            // if there is no content disposition header and content type application/octet-stream
+            // if there is no content disposition header and content type 'application/octet-stream'
             // is handled like an attachment by the browsers
             // https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types#applicationoctet-stream
             // They treat it as if the Content-Disposition header was set to attachment, and propose a "Save As" dialog.

src/site/xdoc/filedownload-howto.xml

@@ -88,7 +88,8 @@ try (final WebClient webClient = new WebClient(BrowserVersion.FIREFOX)) {
                     The AttachmentHandler based download support works in addition to the default UnexpectedPage based support. This means, if your AttachmentHandler
                     does not handle the content, the webClient will fall back to the default solution and place an UnexpectedPage inside the window.
                     You can overwrite the method isAttachment() in your AttachmentHandler to only handle dedicated responses - the default implementation
-                    only detects responses having a content-disposition header of type 'attachment'.
+                    only detects responses having a content-disposition header of type 'attachment' or having no content-disposition header at all and
+                    and content-type header of 'application/octet-stream'.
                 </p>
                 <p>
                     The method <source><![CDATA[boolean handleAttachment(final WebResponse response, final String attachmentFilename)]]></source>