You can use the mark tag to highlight text.

This line of text is meant to be treated as deleted text.

This line of text is meant to be treated as no longer accurate.

This line of text is meant to be treated as an addition to the document.

This line of text will render as underlined.

This line of text is meant to be treated as fine print.

This line rendered as bold text.

This line rendered as italicized text.