This plugin does exactly what it says on the tin – it fades elements in and out, using CSS transitions. You can control the following properties: duration, delay and easing (which must be a valid CSS transition timing function, and defaults to linear).
The duration property is in milliseconds, and defaults to 300 (you can also use fast or slow instead of a millisecond value, which equate to 200 and 600 respectively). As a shorthand, you can use intro='fade:500' instead of intro='fade:{"duration":500}' – this applies to many other transition plugins as well.
If an element has an opacity other than 1 (whether directly, because of an inline style, or indirectly because of a CSS rule), it will be respected. You can override the target opacity of an intro fade by specifying a to property between 0 and 1.