Parameters send information to a function, and then the function executes the code. Functions can use anywhere from zero parameters to a whole list of them. In Example 5-1, you’ll use the echo function to display some text. echo displays text that you send to it as a parameter. Most functions require you to place their parameters inside of parentheses, but echo is an exception to this rule. Echoing of all variables is nearly foolproof!
(From Learning PHP & MySQL by Michele E. Davis, Jon A. Phillips, p. 86)
I don't understand what it really says. Maybe it's better to say echoing variables is nearly foolproof!?