Operable - Accessibility 编辑

When entering a section of functionality using the keyboard, you should be able to get out of that section again using *only* the keyboard. For example, if you press Enter/Return on a focused button to open an options window, you should be able to close that window again and return to the main content using the keyboard.

This is very important so that keyboard users do not get trapped on specific sections of your apps.

For functionality with time limits (e.g. completing a hotel or flight booking often has a time limit), the user should be given controls to allow them to adjust, extend or turn off the time limit.

Exceptions to this are activities with time limits longer than 20 hours, real time events (e.g. live multiplayer games), and any other activity that requires a time limit and would be invalidated if it were turned off.

For moving/blinking content that starts automatically, lasts longer than 5 seconds, and is shown alongside other content, controls should be provided to pause, stop, or hide it. This does not apply to moving/blinking content that is essential to the experience. Examples include scrolling text and videos.

For auto-updating information that starts automatically and is shown alongside other content, controls should be provided to pause, stop, or hide it, or to control the frequency of updates. This does not apply to auto-updating content that is essential to the experience. Examples include carousels or rotating annoucements.

If there is a timeout (caused by user inactivity) warn users at the start of a process so they will not be surprised that a timeout exists (or only allow the timeout to occur after 20 hours of inactivity. 

A mechanism should be provided that allows the user to skip straight to the main content or functionality available on the page, past the repeated features (such as the company logo or navigation). This is often achieved using "skip links" — links put at the top of the page source that link to the main content and are hidden by CSS.

If a proper structure of headings and semantic containers is provided to navigate with (for example <section>, <aside>, etc.), then an added "skip link" is not needed.

You should provide at least two general navigation mechanisms to find pages on your web site, for example navigation menu, breadcrumb trail, site search, site map, list of related links, etc.

The only exception to this is where a page is one step in a process, so should only logically have links to the previous and next steps.

See UI controls, Meaningful text labels, The basics of headings and paragraphs, The <label> element.

Note that you should avoid duplicating headings or labels (e.g. multiple instances of "Further information"), unless the structure allows you to differentiate between them easily.

As well as creating a useful document structure, headings should also accurately describe and break up content areas into logical sections.

Note that this criterion refers to headings and titles in general web content (e.g. headings within text content). Headings and titles for user interfaces are a special case covered in criterion 4.1.2.

See The basics of headings and paragraphs.