CSSRulesubtypen

CSSRulesubtypen is a concept used to describe the different concrete interfaces that represent specific kinds of CSS rules within the CSS Object Model (CSSOM). In the CSSOM, CSSRule serves as a common base type for all rules in a style sheet, and its subtypes correspond to the various forms that a rule can take, such as standard style rules or various at-rule blocks. Each subtype exposes properties and behavior tailored to the kind of rule it represents.

Common subtypes include CSSStyleRule for standard selector and declaration blocks, CSSCharsetRule for @charset, CSSImportRule for @import, CSSMediaRule for @media blocks, CSSFontFaceRule for @font-face, CSSPageRule for @page, CSSKeyframesRule for @keyframes, and CSSKeyframeRule for individual keyframes. Other subtypes that may appear in different contexts include CSSNamespaceRule, CSSSupportsRule, CSSCounterStyleRule, and CSSViewportRule. There is also CSSUnknownRule used for rules that are not recognized by the current implementation.

The type property on a CSSRule instance identifies its subtype numerically, while the specific interface (for example, CSSStyleRule or CSSMediaRule) determines the available properties. For instance, a CSSStyleRule has selectorText and style, whereas a CSSMediaRule has media and cssRules (a nested list of rules within the media block).

Access and manipulation typically occur through the CSSOM from JavaScript, such as iterating document.styleSheets[i].cssRules and inspecting each rule, then using the corresponding interface to read or modify properties. While powerful, the CSSOM heritage varies across browsers, and support for some subtypes may differ.

See also: CSS Object Model, CSSRule, CSSStyleRule, CSSMediaRule.