“ E=MC2 Note that in the first case, the mouse hover tooltip is the Unicode version of the term, as given in the |title=, while in the latter it is the definition given in the |2= parameter.
Linked version:
[ [Mass–energy equivalence|{{dfn|1=E=MC2|2=Mass–energy equivalence; E is energy, m is mass, and c is the speed of light in a vacuum|title=E=MC2}}] ] gives:
E=MC2 It still has a dotted underline indicating a tooltip, but is also a bluelink. Mouse hovering shows both the tooltip and, in the status bar, the target URL, in browsers that support these features. ”

“ The template can be adapted to most directly editable cases in which the <dfn> element would be useful.
Because the definition parameter's content is not readily accessible to users of most if not all screen reader software, text-only browsers, mobile phone browsers, etc., the second parameter should never be used to provide information vital to understanding the article subject, only convenient or augmenting for those who can access it; vital information belongs in the main article prose. ”

“ This template should not be used for marking up glossary entries or links to them; see {{term}} and {{glossary link}} instead, respectively. Likewise, this template should not be used to mark up the bold-faced article subject in the lead; [it is anticipated that] another template, [name forthcoming, probably Template:Subject] , is [to be created to be] used for this purpose, including the needed bold-facing and [perhaps] other markup and metadata features. ”