The style of presentation of a document is an art, the art of graphic design.
Different designers may make different choices, but the ultimate test is usefulness. Can the reader find the information? Does it make sense? Is it accurate?
Accuracy is not a style issue. Clarity is not primarily a style issue, but poor style can ruin clarity. The sections that follow discuss the author's decisions and prejudices that went into the current DocBook customization.
A good first book on graphic layout is The non-designer's design book by Robin Williams, Peachpit Press, ISBN 0321193857. Many of the principles below come straight out of this book.
A font change should be obvious. In many text fonts, the distinction between normal weight and boldface is relatively subtle. Italics stand out a lot more. When available, extra-bold weights will also work. The idea is to give the reader a big cue and not a subtle one.
The current preferred regular body face is Palatino. It may not be the trendy face, but it's clean and easy to read. The actual face is Palladio, a free public-domain face very close to Palatino.
Headings are currently set in Helvetica for lack of anything better.
For monospaced font, the author is severely prejudiced against the universally used Courier face, considering it one of the ugliest fonts in the history of fonts. Fortunately, the free public-domain Vera Sans Mono is both readable and attractive.
The author's favorite monospaced font is Lucida Typewriter, but this is a proprietary font. The open-source, free Luxi family includes a font called LuxiMono, which is pretty close, but it has one fatal flaw: one cannot tell 0 from O. Vera Sans Mono makes this distinction clear by placing a small hyphen inside the zero; this is not to everyone's taste, but clarity trumps taste here, in the absence of a choice that has both.
The Gnu project has a promising new font named Liberation Mono. It is attractive, but it too suffers from the lack of distinction between 0 and O. The author has received a personal communication around late 2007 from that project acknowledging this problem and promising that it will be remedied in a future version.
Certain elements, such as DocBook's
<application> element for
the names of programs, and its
<guibutton> element for
buttons in graphical user interfaces, are set in a
sans-serif face to make them stand out.
One of Williams's best general rules is to use empty space to help the reader make associations. For example, in a list of terms with definitions like this:
A dried bracket fungus.
Red Szechwan peppercorns.
Notice how the definition is close to the term, while there is extra space before each term, so the reader can see which two elements go together.
The indentation structure sets the definition off from the term.