Use the Blind Visualization View to learn how blind users who rely on voice browsers experience webpages. The sections that follow describe common issues that present accessibility and usability challenges for blind users and show how to address these challenges. (Problems are listed in the Problem pane. Clicking the line that describes the problem causes the corresponding element to be highlighted.)
Reaching time refers to the amount of time required to read up to an element on a page. If a page is long and has no intra-page links to facilitate navigation, blind users will find the content difficult to follow. In ACTF, an unacceptably long reaching time is conveyed by dark stripes across the Visualization pane and a red frowning face. By default, the maximum acceptable reaching time is 90 seconds and is conveyed by a black stripe. Anything in excess of that is unacceptable and should be changed.
To address reaching time problems, webpages can be structured by using heading tags and by adding intra-page links so that users can navigate more quickly.
The ACTF checks for the existence of a "skip-to-main-content link." Providing such a link in a webpage allows blind people to jump directly from the top to the main content of the page.
Pages that are long should have internal links with clearly designated destination points, and ACTF also detects intra-page links without destinations and intra-page links without readable text at their source locations. Authors make sure that the destinations of intra-page links are correct by checking the arrow lines and by looking at the background colors of the areas of the page.
The ACTF detects redundant text information. For example, an icon whose ALT attribute is "BluePages" followed by the text string "BluePages" provides redundant information. In this case, voice browsers read this as "Bluepages Bluepages," which is confusing. The ALT attribute of such an icon should be null text. If ACTF detects this on a webpage, the redundancy should be removed.
Alternative text used to describe graphics must be meaningful. Text such as "Spacer" to indicate a spacer image (an image used to create space for some layout purpose) is inappropriate, because such information is useless and irritating for blind people. In such cases, the null text "" is appropriate as the ALT attribute.
The <TABLE> tags are used to create both data tables and layout tables. In both cases, they may cause usability problems for blind users because the reading order of a voice browser is often different from the intuition of sighted people. The ACTF Blind Visualization has a function to draw borders for the table cells, thus allowing an author to check the table structure of the target page.
Nested tables can be difficult for voice browsers to read and for blind listeners to understand because they do not include table headers. Avoid using nested tables for layout purposes.
The structure of the HTML document can be visualized by coloring accessible tags and by showing the table cell structure. All tables must have headers, which ACTF Blind Visualization presents in green in the Visualization pane. Heading tags are presented in blue. Heading tags help structure the page. Tables that are not tagged are difficult for blind readers to visualize.
The tool checks the target page's compliance with accessibility guidelines just as conventional accessibility checkers do. Refer to Compliance and accessibility guidelines for Web content.
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