These all require start and end tags, e.g.
This has some <B>bold text</B>.
Text level elements must be properly nested - the following is in error:
This has some <B>bold and <I></B>italic text</I>.
User agents should do their best to respect nested emphasis, e.g.
This has some <B>bold and <I>italic text</I></B>.
Where the available fonts are restricted or for speech output, alternative means should be used for rendering differences in emphasis.
Note: future revisions to HTML may be phase out STRIKE in favor of the more concise "S" tag from HTML 3.0.