PHP: function with equality sign as parameter?

Question

Can someone explain to me a variable declaration inside a definition of a function, like the one below. What's the purpose? The coding language I use is PHP.

function parse( $filename=FALSE ) {
//some code
}

Answer 1

That is a default value for the function. So if you call parse(), then $filename will be FALSE. However, you could also call parse("/path/to/my/file") and then $filename will contain "/path/to/my/file"