bootstrap: Incorrect usage of the small element as subtext

The suggested usage of the <small> element within a <h> element in order to markup a subtext is incorrect usage of the <small> element.

The HTML5 specification states that:

The small element represents side comments such as small print.

It then gives examples of small print:

Small print typically features disclaimers, caveats, legal restrictions, or copyrights. Small print is also sometimes used for attribution, or for satisfying licensing requirements.

A subtitle or subtext within a <h> element does not match the specification definition of small print and therefore the <small> should not be used in this manner.