Relying on the title attribute is currently discouraged as many user agents do not expose the attribute in an accessible manner as required by this specification (e.g., requiring a pointing device such as a mouse to cause a tooltip to appear, which excludes keyboard-only users and touch-only users, such as anyone with a modern phone or tablet).
This page is about the title attribute, not the <title>-element.
In frames and iframes for a descriptive
Don't use title-attributes
On all other elements.
Source: HTML 5.2: The title attribute