MDN will switch to a new design later today, a sneak peek:

Type: string
Used to set the text which appears in the tooltip when the user moves the mouse over the element. This can be used instead of setting the tooltip to a popup for the common case where it contains only text. The tooltip is displayed in a default tooltip which displays only a label, however the default tooltip may be changed by setting the default attribute on a tooltip element.

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 Contributors to this page: Sheppy, Marsf, Mgjbot, Ptak82, David.humphrey, Dria
 Last updated by: Sheppy,