Since none of the existing on-line presentation software has been found to be accessible to keyboard navigation and screen reader users, none of the Web technologies used in this applications (HTML, Flash or Silverlight) clearly stands out as the technology of choice to achieve accessibility in a presentation software. A deeper comparison of has thus to be undertaken.
What makes an application accessible?
Accessibility is a general term used to describe the degree to which a product (e.g., device, service, environment) is accessible by as many people as possible.
― Wikipedia, The Free Encyclopedia
It is important to note that accessibility concerns are not oriented only oriented toward people with disabilities in its common sense. To some extent, everybody has some disabilities when it comes to using a computer application: most elderly people don’t have heavy sight problems but they might just be reluctant to use them because of the technological barrier, children might prefer to go out and play football rather than seat in front of a screen, businessmen might be using a mobile device with a small screen without a real keyboard… The finiteness is anyway a handicap shared by all humans: there is so much to do, so little time.
To the variety of individuals corresponds a variety of expectations against which the accessibility of the application will be evaluated: the elderlies are likely to prefer simplified software, children might be more keen on the ones that are enjoyable, whereas professionals are looking for powerful applications that do not make them waste their time. Accessibility can thus encompass notions such as usability, hedonistic, usefulness. From this point of view, technologies that help produce highly visual and dynamic applications might, for a particular user target, be the most accessible ones, despite their lack of compatibility with screen readers.
What makes a presentation software accessible?
A presentation software is multiform: it consists of different interfaces to manage, display and edit presentations, as well as the documents themselves. No claim of accessibility could be made unless both the interface and the content are accessible.
User Interface Accessibility
In all studied software packages, the main purpose of the management interface as well as the player is to allow the user to navigate through a set of documents or the different parts of a document. This navigation is usually possible both by using a pointing device and clicking on navigation buttons (play this presentation, display the next slide) or by using keyboard alternatives. The three aforementioned Web technologies all offer mechanism to make those controls accessible to visually impaired users: in all cases, text alternatives can be assigned to the buttons by the developers and this text as well as other textual elements of the page can be read aloud by screen readers.
The main purpose of the authoring part of a presentation software is to allow users to compose a slide by placing different kinds of elements (titles, bullet-points, quotations, images, graphs) in a particular layout. As pointed out in the project specifications, an important part of the information in presentations is carried out visually. It might be possible to create a presentation authoring tool specially for visually impaired users. Adapting a traditional one to those users seems however almost as challenging as adapting a drawing package for blind users, the issue here being rather a matter of usability than a technical one.
There is a lack of comparison of the animation possibilities and performances of those three technologies in the literature. It is thus hard to guess if the effects will always be smooth and not exceed the resources of low-end hardware.
Content Accessibility – Text and Images
As pinpointed in the project specifications, the nature of information in a slide is textual and visual. If the text is accessible to visually impaired users through assistive technologies and to Web crawlers, the purely visual information is not.
Although it is possible to provide textual alternative for non-textual content using Flash or Silverlight, there is no way to preserve the distinction between titles, paragraphs, bullet-points and quotations.
In HTML however, the content is surrounded by semantic tags, i.e. indications about the nature of the text. The following slide…
… could be written as follows in HTML4 …
<!-- The title of the slide is a heading of second level -->
<h2>A Cat's Guide to World Dominashun</h2>
<!-- bullet-points are nested in an Unordered List... -->
<ul> <!-- ...as List Items -->
<li>Be careful, some are laready suspicious:</li>
<!-- The following tag is rather self-explanatory -->
In ancient times, cats were worshiped as gods.
They have never forgotten this.
― Terry Pratchett
<!-- this tag indicates the end of the quote -->
<!-- note the / at the begining of the closing tags -->
This added structure and semantic is used by the screen reader which will state, while reading the content, that the first line is a heading, the following is a bullet point, followed by a block-quote, etc… Using a screen reader, it is also possible to jump from heading to heading using a keyboard shortcut and to use possible internal links to access directly the navigation menu. When the query “world dominashun” is typed in Google, the first results will be pages that have those two words in their headings, because they have a higher importance than if they were used in a paragraph.
The section element represents a generic document or application section. A section, in this context, is a thematic grouping of content, typically with a heading, possibly with a footer.
The article element represents a section of a page that consists of a composition that forms an independent part of a document, page, or site. This could be a forum post, a magazine or newspaper article, a Web log entry, a user-submitted comment, or any other independent item of content.
The section tag seems appropriate for the slides and the article tag seems appropriate for the presentation. All current browsers but Internet Explorer are able to deal with unknown tags. In the latter, a special script has to be used before being able to style the elements. Those elements are not yet recognised by assistive technologies either and are currently ignored.
Content Accessibility – Vector Graphics
In addition to text and image elements, users should be able to use vector graphics to create chart and diagrams in a slide. This would effectively make ToDoSo useful for a large variety of professional users.
Vector Graphics are traditionally the prerogative of Flash as browser vendors never agreed on a common standard. Despite being not interoperable, all browsers have native vector graphics capabilities which integrates with HTML. Just like Flash, Silverlight provide the possibility to create and manipulate vector graphics.