Blink element



The blink element is a non-standard presentational HTML element that indicates to a user agent (generally a web browser) that the page author intends the content of the element to blink (that is, alternate between being visible and invisible). The element was introduced in Netscape Navigator and has some support in other web browsers, but support for the feature is absent from Internet Explorer.

Despite the element being initially popular amongst personal homepages, it has since fallen out of favor due to its overuse and the difficulty it presents in reading. The tag achieved notoriety for being extremely user-unfriendly.

Lou Montulli is credited as the inventor of the blink tag at Netscape, although he only suggested the idea, without writing any actual code.

Usage
The blink element is non-standard, and as such there is no authoritative specification of its syntax. While Bert Bos of the World Wide Web Consortium has produced a Document Type Definition that includes syntax for the blink element (defining it as a phrase element on a par with elements for emphasis and citations), the comments in the DTD explain that it is intended as a joke.

Syntax of the blink element type is identical to such standard HTML inline elements as span. For example:.

The rate of blinking is browser-specific. In Mozilla Firefox the text alternates between being visible for three quarters of a second and being invisible for one quarter of a second.

The blink element type was first invented for Netscape Navigator and is still supported in its descendants, such as Mozilla Firefox (except for the Netscape 6 and early Mozilla suite browsers). It is also supported by the Opera Internet Browser. Microsoft's Internet Explorer and Apple's Safari/WebKit do not support it, even in its CSS incarnation.

Implementation
The blink value of the CSS text-decoration property allows authors to suggest that text should blink without using proprietary tags, but the CSS 2.1 Specification states that "conforming user agents may simply not blink the text" in order to comply with the User Agent Accessibility Guidelines.

Example:

Usability and accessibility
The blink element has been consistently criticised by usability and accessibility experts. In 1996 Jakob Nielsen described the element as "simply evil" in his Alertbox column Top Ten Mistakes in Web Design.

The World Wide Web Consortium's Web Content Accessibility Guidelines 1.0 state that content authors should avoid causing the screen to flicker or blink, noting that such effects can cause problems for people with cognitive disabilities or photosensitive epilepsy.

The German Federal Government's Barrierefreie Informationstechnik-Verordnung (Barrier-free Information Technology Ordinance) also states that flickering or blinking content should be avoided.

The United States Federal Government's Section 508 states that pages should avoid causing the screen to flicker with a frequency between 2 Hz and 55 Hz, a range which covers rapidly blinking text.

To comply with the User Agent Accessibility Guidelines a user agent must either "allow configuration to render animated or blinking text content as motionless, unblinking text" or never blink text. Mozilla Firefox satisfies this requirement by providing a hidden configuration option to disable blinking.