The following typographical conventions are used in this book:
Used for filenames and directory names , programs, compilers, tools, utilities, URLs, emphasis, and first use of a technical term .
Used in code examples and to show the contents of files. Also used for tags, attributes, and environment variable names appearing in the text.
Used as a placeholder to indicate an item that should be replaced with an actual value in your program.
Constant width bold
Used to highlight a particular section or change in code, such as a custom tag or a change in a transaction.