STRONG is for importance
The "strong" element is for indicating that a word or phrase within a sentence has strong importance, urgency or seriousness.
This is typically conveyed with typography by applying a font weight to the strong phrase that is heavier than its surrounding text, but other CSS styling may serve the purpose better.
Importance as used here is not the same as embolden as used with the "b" element.
- The "b" element is for stylistically treating a word or phrase as being somehow different from the rest, by using a heavier font weight than the surrounding text.
- The "i" element is for stylistically treating a word or phrase as being somehow different from the rest, by using an italicized variant of the font.
- The "em" element is for emphasizing a word or phrase within a sentence, suggesting that the reader should use an emphatic tone of voice.