Variants of Hiding Element

Mechanisms for Hiding Content

CSS Rules	Display Effect	Accessibility Effect
visibility: hidden;	Element is hidden from view, but is not removed from the normal flow (i.e., it still takes up the space it normally would)	Content is ignored by screen readers
display: none;	Element is removed from the normal flow and hidden; the space it occupied is collapsed	Content is ignored by screen readers
height: 0; width: 0; overflow: hidden;	Element is collapsed and contents are hidden	Content is ignored by screen readers
text-indent: -999em;	Contents are shifted off-screen and hidden from view, but links may “focus” oddly and negative indent may not prove long enough to fully hide content	Screen readers have access to the content, but the content is limited to text and inline elements
position: absolute; left: -999em;	Content is removed from the normal flow and shifted off the left-hand edge; the space it occupied is collapsed	Screen readers have access to the content

Good Reference : http://snook.ca/archives/html_and_css/hiding-content-for-accessibility