The HTML <abbr> Element (or HTML Abbreviation Element) represents an abbreviation and optionally provides a full description for it. If present, the title attribute must contain this full description and nothing else.

Usage note:
When present, the grammatical number of the text in the title attribute should match that of the content of the <abbr> element. This is also the case in languages with more than two grammatical numbers (for example, Arabic not only has singular and plural categories, but also a dual category).

Content categories:
Flow content, phrasing content, palpable content

Permitted content:
Phrasing content.

Tag omission:
None, both the starting and ending tag are mandatory.

Permitted parent elements:
Any element that accepts phrasing content.

DOM interface:
HTMLElement Up to Gecko 1.9.2 (Firefox 3.6) inclusive, Firefox implemented the HTMLSpanElement interface for this element.

Default styling:
The purpose of this element is purely for the convenience of the author and all browsers display it inline (display: inline) by default, though its default styling varies from one browser to another:

Some browsers, like Internet Explorer, do not style it differently than a <span> element.
Opera, Firefox, and some others add a dotted underline to the content of the element.
A few browsers not only add a dotted underline, but also put it in small caps; to avoid this styling, adding something like font-variant: none in the CSS takes care of this case.
