Which of the examples is considered to be semantically correct?
<a href="http://example.com/"><strong>Example</strong></a><strong><a href="http://example.com/">Example</a></strong>
Of course applies to any other formatting tag like <u>, <em> etc.
Both are correct. both are inline elements which can contain other inline elements (except there own tag)
<strong><strong></strong></strong>is incorrect but any of this list can be used inside of each other.