In tra­di­tional print­ing ter­mi­nol­ogy, a rule is a line; a bor­der is a box. But in word proces­sors and web browsers, they’re vari­a­tions of the same func­tion. Rules and bor­ders can be ap­plied to pages, para­graphs, or ta­bles.

Like cen­tered text, bold or italic, and all caps, rules and bor­ders are best used spar­ingly. Ask your­self: do you really need a rule or bor­der to make a vi­sual dis­tinc­tion? You can usu­ally get equally good re­sults by in­creas­ing the space above and be­low the text. Try that first.

For bor­ders, set the thick­ness be­tween half a point and one point. Thin­ner bor­ders can work on pro­fes­sion­ally printed goods but are too fine to re­pro­duce well on an of­fice printer. Thicker bor­ders are coun­ter­pro­duc­tive—they cre­ate noise that up­stages the in­for­ma­tion in­side. You want to see the data, not the lines around the data.

Sim­i­larly, don’t use pat­terned bor­ders (i.e., any­thing other than a sin­gle solid line, like dots, dashes, or dou­ble lines). They’re un­nec­es­sar­ily complicated.

With rules, you have more lat­i­tude be­cause they don’t ac­cu­mu­late the way bor­ders do. If you want to make a rule thicker than one point or use a pat­tern, go ahead. But thick or pat­terned rules still wear out their wel­come faster than the clas­sic half-point solid rule.

Never make rules and bor­ders out of re­peated ty­po­graphic char­ac­ters, like punc­tu­a­tion, hy­phens and dashes, or math sym­bols. Es­pe­cially ridicu­lous is the habit of us­ing stacked paren­the­ses or sec­tion marks to make a ver­ti­cal line on cap­tion pages. Not only is it uglier than a ver­ti­cal rule, it’s much harder to as­sem­ble. These are type­writer habits. They’re obsolete.