I use the following font conventions in this book.
Italic is used for:
Unix pathnames, filenames, and program names
Internet addresses, such as domain names and URLs
New terms where they are defined
Boldface is used for:
Names of GUI items: window names, buttons , menu choices, etc.
Constant width is used for:
Command lines and options that should be typed verbatim
Names and keywords in Java programs, including method names, variable names, and class names
XML element tags