::=

The element to the left of the symbol is defined by the constructs on the right. 

*

The preceding construct may occur zero or more times. 

{...}

The constructs within the curly braces are grouped together. 

[...]

The constructs within the square brackets are optional. 

|

An exclusive OR.

BOLDFACE

A keyword (although capitalized in the BNF diagram, keywords are not case-sensitive). 

White space 

A white space character can be a space, a horizontal tab, or a line feed.