A collection of style sheet rules.
|JScript - 3.0|
|Internet Explorer - 4.0|
This is sometimes referred to as a rules object which is not strictly true. It is often so named because it is referenced by the rules property of a stylesheet.
DOM level 2 describes this object as a CSSRuleList object. It implies it is a sub-class of the Collection object and therefore it supports the item() method.