Usablenet Assistive User's Manual
101 Avenue of the Americas - Suite 1201, New York, NY 10013, USA
Ph: +1 (212) 965 5388
Fax: +1 (212) 965 5391
- 1. What's Usablenet Assistive and how does it work?
- 2. Using Usablenet Assistive
- 3. Setting your preferences
- 4. Privacy aspects
- 5. Security aspects
Usablenet Assistive (or transcoder) is a web application that
converts a web page into its text-only version on-the-fly by eliminating
all page layout that is present in the original page and by
hiding many accessibility defects.
The transcoder is useful for the website visitor, since it removes some accessibility issues and small defects like missing image ALTs or forms that are not properly linearized or flash objects. It can be used also by the web developer to determine if the reading order of the information presented in the page makes sense when read in the order that would be followed by a screen reader or speech browser.
Usablenet Assistive is especially useful for people and situations where:
- graphics cannot be seen (e.g. blind persons, text-only browsers, ...);
- sizes of the page elements have to changed (e.g. a low-vision persons that maximizes the browser windows to enlarge its contents; a PDA user who has to fit everything on a small screen);
- size of text that has to be changed (e.g. a low-vision person; a presenter that has to project a web page to an audience via a projector);
- links and buttons have to be easily located and operated (e.g. a person with motor disabilities that cannot move his/her hand with precision, like somebody with a broken arm);
- form fields need to be easily laid out to be used (e.g. a low vision person using a screen magnifier that restricts his/her field of vision).
Usablenet Assistive yields pages that are more in compliance to Section 508 and WCAG AA guidelines than the original ones. To do so, it performs a number of transformations on the web page layout and content:
- transcoded pages are based on CSS and do not constrain character size nor font family; their page layout is fluid that is fully adaptable to the visitor's browser window;
- automatic redirects implemented with META tags are substituted with server-based redirect (i.e. the browser will be automatically redirected to the required URL); in this way users would not perceive these redirects at all;
- the transcoder puts three spaces between links that are too close; in this way links are well separated and it is easier to select each of them;
- all scripts and style sheets are removed; scripts are replaced by the content of the NOSCRIPT tag if it exists;
- frames and framesets are replaced by a page that can simultaneously display (in text-mode) all the content of all the frames. In this way a user can get the entire content at once (as she/he does when using a frame-enabled graphical browser). Inter-frame navigation works as it should.
- NOFRAMES elements are not used at all;
- all layout tables are linearized. If a table is recognized as a data table, the transcoder keeps its original markup, since the resulting page is easier to read;
- images are replaced by their ALT. If no ALT is provided for the image, but a TITLE attribute exists, then TITLE is used in the resulting page. They are removed if no ALT or TITLE is specified; if the image is used as a button and it does not contain an ALT or a TITLE, it is substituted by "Go to URL-LOCATION." where URL-LOCATION is the URL pointed to by the button;
- client side image maps are transformed into simple lists of the links contained in AREA elements; if the ALT or TITLE of the image is defined, it is used as for the navigation bar. The ALT tag of each AREA element is used as label for its link. If ALT is not provided, a "Go to URL." link is added;
- graphical submit buttons in forms are substituted with textual buttons; a textual button label is obtained from ALT attribute if it is present; otherwise the word "submit" is used;
- inline frames are substituted with links to the documents they are referring;
- meta keywords and meta descriptions are not changed;
- objects are substituted with the text-only version of their content, if any; objects are removed otherwise;
- applets are substituted with the text-only version of their content; if an applet has no content, the ALT attribute is used; otherwise applets are removed;
- form controls and labels that are correctly marked up are linearized by Usablenet Assistive with a a proper positioning of labels with respect to the controls they refer to. In particular the content of the LABEL tag is placed before or after the form control it refers to (depending on whether the control is a text field, radio button, checkbox or select menu). If no LABEL is specified but TITLE is given, then the content of TITLE is placed before or after the control;
Usablenet Assistive adds new CSS rules to the output page to let the user
change color theme and font size of the web page.
These settings are saved using cookies and therefore are available to a Usablenet Assistive user (if cookies are enabled by his/her browser).
The transcoder is able to process any page on the Internet. It currently can transcode pages whose content is based on:
- HTTP and HTTPS protocols;
- GET or POST methods to send request parameters;
- HTTP Basic Authentication and NTLM authentication;
If a framed page contains two frames requiring HTTP Base Authentication,
Usablenet Assistive will open a connection only to the first frame for security reasons.
See the Security section for more details about how Usablenet Assistive supports secure connections.
While Usablenet Assistive is very efficient, to transcode a page it has to:
- receive a request from the visitor's browser,
- issue a request to the webserver hosting the site,
- wait for the webserver and the network to yield the data,
- transform the page, and finally
- send the transformed page to the user's browser.
Figure 1: Interaction between browser, transcoder and web server
The response time for getting a text-only page (i.e. the time the web
visitor has to wait to see some results), compared to the time to get
the original page, is affected by steps 2, 3 and 4.
Depending on whether the transcoder is installed in the same local network as the webserver or in a different network, the performance will differ (the latter case is the worst as steps 2 and 3 require more time).
Using Usablenet Assistive is straightforward: once you activate a "text-only" link that is based on Usablenet Assistive, or after you use the form in the Main page, your browser will display the transcoded page. Most of the links that you can select will activate again Usablenet Assistive: when you select any of them, your browser will display the transcoded page.
To achieve this effect the transcoder does what is called URL remapping. In fact Usablenet Assistive, besides performing a number of changes to the content of the page (as described in the Layout and content transformations subsection), changes also most of the URLs of the links and form actions in such a way that your browser sends the requests to Usablenet Assistive rather than the web server. Usablenet Assistive then relays the request to the web server, gets the answer, processes it and hands it to your browser.
The webmaster managing the web server hosting the "text-only" links or the Main page can decide where to stop this URL remapping. (Consider that if there are no such limits then you would be able to navigate through the entire Internet via Usablenet Assistive.) When the border is reached (and it depends on how Usablenet Assistive has been configured by the webmaster running it), Usablenet Assistive does not remap URLs any further. Typically a border is crossed when the webserver changes. For example, you might be able to use Usablenet Assistive on pages hosted by www.anycompany.com. If some of the pages contain links to news.anycompany.com, then Usablenet Assistive may refuse to remap these links because they exit from the server for which Usablenet Assistive has been configured. The webmaster can configure Usablenet Assistive so that any other link can be prevented from being remapped by Usablenet Assistive.
The webmaster can also customize Usablenet Assistive and change the default way for displaying a text-only page. Usually this is done for forms, for navigation bars and for special sections within pages for which the webmaster has some special requirement.
Usablenet Assistive can produce error messages. This happens when Usablenet Assistive encounters anomalous situations in talking with the web server that should supply the page (for example the requested page cannot be delivered by the web server). These errors are displayed as shown in figure.
Figure 2: File not found error message of Usablenet Assistive
Very rarely Usablenet Assistive may face weird situations and generate an error, even when a proper communication with the web server and the browser was in place. These errors include "Internal error" and are displayed as shown in figure.
Figure 3: Internal error message of Usablenet Assistive
When you need to browse websites that are behind a password authentication based on HTTP, Usablenet Assistive simply acts as a web proxy. This means that the browser will ask you to enter your username and password (required to access the website) and it will send the data to Usablenet Assistive, which in turn will send them to the web server. Username and password are not stored by Usablenet Assistive. They are acquired from the browser and sent to the web server through a secure connection (SSL) only if your browser shows HTTPS as a protocol. See the Security aspects and the Privacy aspects sections for more details.
Usablenet Assistive allows you to choose your display preference. These preferences are handled via cookies so that Usablenet Assistive can remember your choices. You must enable cookies in your browser.
Display preferences can be selected in a section entitled
Text Only Options located at the bottom of any
Hold down ALT key and press T to jump to the Text Only Options section.
If you are using Internet Explorer, you must hold down ALT key, press T and then press enter key to obtain the same result.
If your browser has a menu with T as shortcut (for example 'Tools' in Internet Explorer) you can still open it using the keyboard by pressing ALT key and T separately.
The last part of Text Only Options section can be used to view the original version of the transcoded page, to launch Usablenet Assistive on any other public web page and to view the Usablenet Assistive Main Page.
Figure 4: Preferences affecting the behaviour of Usablenet Assistive
Within the Text Only Options section you can select the following preferences.
- Font size: to be used when displaying the page content. This is useful for low vision persons or when you need to enlarge the content of a page (for example when projecting a page during a public presentation). Press the "larger" link to enlarge, "smaller" to reduce the size, or "default" to reset it to the default value.
- Color mode: to be used for background and foreground colors. In many cases you might prefer viewing the page content in black over a white background. But sometimes it is easier to read and scan the page if you use inverted colors. Available foreground/background combinations enhance the contrast and are: black on white, yellow on black, black on cream. Feel free to try them all and select the one that looks the best.
- Textual links: to people with motor disabilities (or those using less than optimal pointing devices) moving a pointer on a small link to select it is a complex task, requiring lot of attention and often leading to errors. If you use this option, Usablenet Assistive frames each textual link into a rectangular box and it makes sure that these links stand out clearly from the nearby elements.
- Moving navigation bars to the bottom of the page:
the webmaster can configure Usablenet Assistive to move some objects of the page
(for example the main navigation bar, the search box) to the bottom of
the page. In this way those objects, that usually are repeated all
over the website, are not in the way if you use screen
readers. You get directly to the main content of the page first, and
can still get to these elements by scrolling the page.
However, you can set a preference of Usablenet Assistive to avoid this. Simply set the preference called
Move navbars to the bottom of the page(or
Do not move navbarsto unset it).
- Speedbumps: when deployed, Usablenet Assistive is limited to
registered web servers, in the sense that it will transcode only pages
hosted on web servers that are properly registered. The set of
registered web servers and their pages is called text-mode
realm and it is defined by the webmaster of the website. When you
activate a link that crosses the border of the text-mode realm (i.e. a
link that brings you outside the web servers registered within Usablenet Assistive)
by default Usablenet Assistive will alert you that you are leaving the text-mode
realm and will offer you the choice between navigating in text-mode
but by using a demo service hosted by Usablenet, or switching to
However, you can set the preference called
[Don't] alert me when leaving text-modeso that Usablenet Assistive does not bother you with this alert page. In such a case Usablenet Assistive will switch off (i.e. the linked page will be displayed in graphic-mode by your browser).
If you don't see this preference, it means that the webmaster has not configured Usablenet Assistive to exploit this feature.
- Not handled documents: when you activate a link
that does not refer to a web page, Usablenet Assistive will alert you that it can not
process that page and will propose to download the original file.
You can disable this alert page by setting the preference called
Open not handled documents directly. Set
Show a splash page for not handled documentsto re-enable the alert page.
Figure 5: Display of links for motor-disabled persons and with a yellow on black color mode
Usablenet Assistive has to acquire from the web server the pages it processes,
transform them, and deliver the transformed version to your
browser. And you might be concerned about who can see and what can be
done with that information.
Usablenet Assistive has been designed so that privacy and security issues are minimized.
By design, most of this information is not stored in any permanent form within Usablenet Assistive files. It lives in volatile memory only within the processes implementing the transcoder service and only for a very limited time (a fraction of a second). The only information that is permanently stored is the log of the HTTP/HTTPS requests, which does not include cookies nor form values.
However consider that Usablenet does not necessarily host the
transcoder you are using. (It is easy to check: if the URL of a
transcoded page starts with
http://assistive.usablenet.com:... then it is hosted by
If Usablenet is not hosting Usablenet Assistive (i.e. Usablenet Assistive has been licensed to
another party) then Usablenet cannot give any guarantee in terms of
privacy and security. You should contact the webmaster of the
organization that is hosting Usablenet Assistive (whose domain name appears at the
beginning of the transcoded URLs).
If you are using a transcoder hosted by Usablenet then the only information that is permanently stored is the log of the HTTP/HTTPS requests, which does not include cookies nor form values.
Please contact us at email@example.com for additional information.
Usablenet Assistive works as a web proxy, and when it transcodes a page it has to transform all the URLs of the links and form buttons that are contained in the page. Each URL is transformed (remapping of URLs) so that the request is first filtered by Usablenet Assistive and then it is Usablenet Assistive that issues another request to the original web server.
However when the URLs specify the HTTPS protocol, things become more
complex. Usablenet Assistive has to remap URLs so that both the Internet connections
(the one between the user browser and Usablenet Assistive and the one between Usablenet Assistive
and the web server) are secure (i.e. on a Secure Socket Layer,
SSL). Therefore Usablenet Assistive remaps each HTTPS link into an HTTPS link
pointing to Usablenet Assistive and specified so that the Usablenet Assistive connects to the web
server through HTTPS.
For example the link
is transformed into
(the actual server name for Usablenet Assistive may be different in your case). Notice the two occurrences of "HTTPS".
Security warning: if in your browser you notice that a link contains only one instance of HTTPS (instead of two), it means that the connection between your browser and Usablenet Assistive or the connection between Usablenet Assistive and the web server is not secure. In this case, if you are concerned about security of information exchanged between your browser and the web server, you should not continue your activity. Contact the webmaster responsible for the transcoder.
HTTPS is based on certificates, special files that contain all the
information that allow the two parties in a connection to verify the
identity of each party and to make sure that transit information is
encrypted so that it cannot be tampered.
When you use the browser to open a page with the HTTPS protocol, your browser and the web server exchange also certificates. When a browser receives a certificate from a web server, unless the certificate is signed by an official Certificate Authority (i.e. unless the certificate has been issued by such an authority, usually called public certificates), the browser will tell you that with an appropriate pop-up window.
Usablenet Assistive properly processes secure pages (i.e. it remaps secure pages into secure transcoded pages) only if the webserver uses public certificates. If the webserver requires HTTPS to access a page, but the webserver does not have public certificates, Usablenet Assistive would not transcode the page.
Figure 6: Generic HTTPS error of Usablenet Assistive
In this way Usablenet Assistive behaves as a very conservative browser, refusing to continue a transaction when it is insecure but the Usablenet Assistive user expects it to be carried out securely.