Borders and boxed text
Use borders and boxed text in moderation. A page can look very cluttered when sections of text and illustrations appear in boxes. It can also disrupt the flow of reading. There are other ways to design pages to highlight text but the best policy is to keep it simple (see Emphasising text).
When a block of text has to be highlighted, make sure there is good contrast between the panel and the text so that the words can still be easily read. Remember that tinted and shaded panels don't reproduce well on a photocopier. It is best to avoid panels altogether if your document is likely to be photocopied.
Reversed text, for example white text on a black background, can be used to good effect especially as a form of highlighting in contrast to plain black-on-white text. However, keep it to highlight short passages only - pagefuls of reversed text can be difficult to read - and do not use reversed text for audiences with visual impairments. Make sure the type size and font of the reversed text are large and bold enough so that the text doesn't become indistinct.