In this lesson
- first
The next four pages explain each priniple and associated guidelines plus links to relevant parts of the course
Principle 1 - Is the website Percievable
Guideline 1.1 Provide text alternatives for any non-text content so that it can be changed into other forms people might need, such as large print, braille, speech, symbols or simpler language.
1.1.1 All non-text content that is presented to the user has an alternative text version that serves the equivalent purpose or explains the reason for inclusion. (Level A)
- Use alt attributes on img elements
- Use longdesc or “D” link
- Use alt attributes on images used as submit buttons
- Provide text alternatives for the area elements of image maps
- Provide text alternatives on applet elements (lesson 8 )
- Provide link text that describes the purpose of a link for anchor elements (Lesson 10, section 2 )
- Provide alternative output modes for CAPTCHA (to confirm user is a person not a robot)
- Use CSS to present decorative images so that assistive software ignores the image ( Lesson 7, Section 2)
Guideline 1.2 Provide alternatives for time-based media (Video and audio)
The basic issues in relation to this guideline are addressed in lesson 8 (section 3) . If you are intending to use a lot of multimedia on your website you will need to be aware of the various requirements for whichever technolgies you wish to use.
1.2.1 For pre-recorded audio-only a text alternative is available, and for pre-recorded video-only either a text or audio alternative is available: (Level A)
- For audio containing speech: provide a text transcript, or similar, for deaf people to read. lesson 8 (section 3)
- For video only (i.e no sound track): provide either a text or audio description of the video content so that blind people can hear the audio version or ask their screen reader to read out the text version. lesson 8 (section 3)
1.2.2 Captions are provided for all pre-recorded audio content in synchronised media, except when the media is a media alternative for text and is clearly labelled as such (level A)
- Provide subtitles or captions for pre-recorded video lesson 8 (section 3)
NOTE: The remaining guidelines in this section (1.2.3 to 1.2.9) cover the accessibility of audio and video content when it is synchronised to some other media, or when the media authoring programme has certain tools available. If you are including synchronised video, or intend using a lot of multimedia on your website, you should learn to use SMIL (Synchronized Multimedia Language) so that you can apply the various accessibility options. For more on SMIL accessibility visit the W3C website at http://www.w3.org/TR/SMIL-access/
Guideline 1.3 Create content that can be presented in different ways (for example simpler layout ) without losing information or structure.
1.3.1 Information, structure, and relationships conveyed through presentation can be programmatically determined or are available in text. (Level A)
- Use semantic elements to markup text (Lesson 3, section 1 & 2)
- Use semantic elements to mark up data tables (Lesson 3, section 4 )
- Use semantic elements to mark up forms (Lesson 9)
- Provide a clear relationship between labels and the relavant form controls (Lesson 9 )
1.3.2 When the sequence in which content is presented affects its meaning, a correct reading sequence can be programmatically determined. (Level A)
- HTML presents the correct reading sequence of a page, or individual areas within the page. (Lesson 2, section 3)
- If tables are used for layout they make sense when linearised. ( Lesson 5, Section 1 )
1.3.3 Instructions provided for understanding and operating content do not rely solely on sensory characteristics of components such as shape, size, visual location, orientation, or sound. (Level A)
- Do not rely on the shape, size, sound or position of elements on your page for delivering information or controlling actions.
Guideline 1.4 Make it easier for users to see and hear content including separating foreground from background.
1.4.1 Colour is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element. (Level A)
- Do not rely on the colour of elements on your page for delivering information or controlling actions. ( Lesson 6, section 2 )
1.4.2 If any audio on a Web page plays automatically for more than 3 seconds, either a mechanism is available to pause or stop the audio, or a mechanism is available to control audio volume independently from the overall system volume level. (Level A)
- Allow users to control the volume of sounds and to stop or pause any sound easily ( Lesson 8, section 3 )
1.4.3 The visual presentation of text and images of text has an adequate contrast ratio (Level AA)
- The difference between the foreground and background colours ot text and images must be at least 5:1, and preferrably be better than 7:1. (large text can have a lower contrast ratio ) (Lesson 6, section 2 )
1.4.4 Except for captions and images of text, text can be resized without assistive technology up to 200 percent without loss of content or functionality. (Level AA)
- Use relative dimensioning (e.g. % or em) for defining text sizes ( Lesson 6, section 1 )
1.4.5 If the technologies being used can achieve the visual presentation, text is used to convey information rather than images of text (Level AA)
- images of text should not be used for delivering content or presentations unless essential, in which case suitable text alternatives must be available. (Leson 7 section 1 )
1.4.6 The visual presentation of text and images of text has a contrast ratio of at least 7:1 (Level AAA)
- This action reinforces action 1.4.3 by not accepting contrast ratios less than 7:1 (except for large text) (Lesson 6, section 2 )
1.4.7 For prerecorded audio-only content that (1) contains primarily speech in the foreground, (2) is not an audio CAPTCHA or audio logo, and (3) is not vocalization intended to be primarily musical expression such as singing or rapping, the following is true: (Level AAA)
- The distinction between the background noise and the foreground speech is adequate for people with some limited hearing capability.( lesson 8 (section 3)
1.4.8 For the visual presentation of blocks of text, a mechanism is available to achieve the following: (Level AAA)
- foreground and background colors can be selected by the user (lesson 4, section 1 )
- width is no more than 80 characters (Lesson 6, section 1 )
- text is not justified (aligned to both the left and the right margins) (Lesson 6, section 1 )
- line spacing (leading) is at least space-and-a-half within paragraphs, and paragraph spacing is at least 1.5 times larger than the line spacing (Lesson 6, section 1 )
- text can be resized without assistive technology up to 200 percent in a way that does not require the user to scroll horizontally to read a line of text on a full-screen window (Lesson 6, section 1 )
1.4.9 Images of text are only used for pure decoration or where a particular presentation of text is essential to the information being conveyed. (Level AAA)
- Do not use images of text unless absolutely essential for decorative reasons only (Lesson 7 section 1 )