上海时时乐开奖视频:Accessibility Principles

Web accessibility standards

Web accessibility relies on several components that work together. Some of these include:

More about web accessibility standards

These components inter-relate and support each other. For instance, web content needs to include text alternatives for images. This information needs to be processed by web browsers and then conveyed to assistive technologies, such as screen readers. To create such text alternatives, authors need authoring tools that support them to do so. More background is provided in Essential Components of Web Accessibility.

Standards play a vital role in defining accessibility requirements for each of these components. Some accessibility requirements are easy to meet, yet understanding the basics of how people with disabilities use the Web helps implement them more effectively and efficiently. Some aspects of accessibility require more technical skills or advanced knowledge of how people use the Web. In all cases, involving users early and throughout your web projects will make your work better and easier.

The W3C Web Accessibility Initiative (WAI) provides a set of guidelines that are internationally recognized as the standard for web accessibility. These include:

There is also a WAI specification for Accessible Rich Internet Applications (WAI-ARIA), which include dynamic content and advanced user interface controls developed with Ajax, JavaScript, and related web technologies.

Perceivable information and user interface

Text alternatives for non-text content

Text alternatives are equivalents for non-text content. Examples include:

Text alternatives convey the purpose of an image or function to provide an equivalent user experience. For instance, an appropriate text alternative for a search button would be “search” rather than “magnifying lens”.

Text alternatives can be presented in a variety of ways. For instance, they can be read aloud for people who cannot see the screen and for people with reading difficulties, enlarged to custom text sizes, or displayed on braille devices. Text alternatives serve as labels for controls and functionality to aid keyboard navigation and navigation by voice recognition (speech input). They also act as labels to identify audio, video, and files in other formats, as well as applications that are embedded as part of a website.

Captions and other alternatives for multimedia

People who cannot hear audio or see video need alternatives. Examples include:

Well-written text transcripts containing the correct sequence of any auditory or visual information provide a basic level of accessibility and facilitate the production of captions and audio descriptions.

Content can be presented in different ways

For users to be able to change the presentation of content, it is necessary that:

Meeting this requirement allows content to be correctly read aloud, enlarged, or adapted to meet the needs and preferences of different people. For instance, it can be presented using custom color combinations, text size, or other styling to facilitate reading. This requirement also facilitates other forms of adaptation, including automatic generation of page outlines and summaries to help people get an overview and to focus on particular parts more easily.

Content is easier to see and hear

Distinguishable content is easier to see and hear. Such content includes:

Meeting this requirement helps separate foreground from background, to make important information more distinguishable. This includes considerations for people who do not use assistive technologies and for people using assistive technologies who may observe interference from prominent audio or visual content in the background. For instance, many people with color blindness do not use any particular tools and rely on a proper design that provides sufficient color contrast between text and its surrounding background. For others, audio that is automatically played could interfere with text-to-speech or with assistive listening devices (ALDs).

Operable user interface and navigation

Functionality is available from a keyboard

Many people do not use the mouse and rely on the keyboard to interact with the Web. This requires keyboard access to all functionality, including form controls, input, and other user interface components.

Keyboard accessibility includes:

Meeting this requirement helps keyboard users, including people using alternative keyboards such as keyboards with ergonomic layouts, on-screen keyboards, or switch devices. It also helps people using voice recognition (speech input) to operate websites and to dictate text through the keyboard interface.

Users have enough time to read and use the content

Some people need more time than others to read and use the content. For instance, some people require more time to type text, understand instructions, operate controls, or to otherwise complete tasks on a website.

Examples of providing enough time include providing mechanisms to:

Content does not cause seizures

Content that flashes at certain rates or patterns can cause photosensitive reactions, including seizures. Flashing content is ideally avoided entirely or only used in a way that does not cause known risks.

Well organized content helps users to orient themselves and to navigate effectively. Such content includes:

Meeting this requirement helps people to navigate through web pages in different ways, depending on their particular needs and preferences. For instance, while some people rely on hierarchical navigation structures such as menu bars to find specific web pages, others rely on search functions on websites instead. Some people may be seeing the content while others may be hearing it or seeing and hearing it at the same time. Some people may be using the content with only a mouse or a keyboard, while others may be using both.

Understandable information and user interface

Text is readable and understandable

Content authors need to ensure that text content is readable and understandable to the broadest audience possible, including when it is read aloud by text-to-speech. Such content includes:

Meeting this requirement helps software, including assistive technology, to process text content correctly. For instance, this requirement helps software to read the content aloud, to generate page summaries, and to provide definitions for unusual words such as technical jargon. It also helps people who have difficulty understanding more complex sentences, phrases, and vocabulary. In particular, it helps people with different types of cognitive disabilities.

Content appears and operates in predictable ways

Many people rely on predictable user interfaces and are disoriented or distracted by inconsistent appearance or behavior. Examples of making content more predictable include:

Meeting this requirement helps people to quickly learn the functionality and navigation mechanisms provided on a website, and to operate them according to their specific needs and preferences. For instance, some people assign personalized shortcut keys to functions they frequently use to enhance keyboard navigation. Others memorize the steps to reach certain pages or to complete processes on a website. Both rely on predictable and consistent functionality.

Users are helped to avoid and correct mistakes

Forms and other interaction can be confusing or difficult to use for many people, and, as a result, they may be more likely to make mistakes. Examples of helping users to avoid and correct mistakes include:

Meeting this requirement helps people who do not see or hear the content, and may not recognize implicit relationships, sequences, and other cues. It also helps people who do not understand the functionality, are disoriented or confused, forget, or make mistakes using forms and interaction for any other reason.

Robust content and reliable interpretation

Content is compatible with current and future user tools

Robust content is compatible with different browsers, assistive technologies, and other user agents. Examples of how this can be achieved include:

Meeting this requirement helps maximize compatibility with current and future user agents, including assistive technologies. In particular, it enables assistive technologies to process the content reliably, and to present or to operate it in different ways. This includes non-standard (scripted) buttons, input fields, and other controls.

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