Computed Field: &$node, $field, and &$node_field ?

The Computed Code help text mentions "The variables available to your code are: &$node, $field, and &$node_field."

• None of the examples I could find include the ampersand, so is the description accurate?
• I'm not sure what '$field' does?
• Could the help text me amended to include examples of all three variables, it would help us novices.