Changes in HTML 5 - <summary> Tag
What's new in HTML 5
Differences between HTML 5 and earlier versions of HTML
The <s> tag and <strike> tag tag were both deprecated in HTML 4, but the <s> tag may now be used in HTML 5 code. The <strike> tag should never be used, and neither it nor the <s> tag should be used in HTML 4 code until the DOCTYPE declaration is modified to convert to HTML 5.