css-extensions.json

{
  "spec": {
    "title": "CSS Extensions",
    "url": "https://drafts.csswg.org/css-extensions-1/"
  },
  "properties": [],
  "atrules": [
    {
      "name": "@custom-selector",
      "href": "https://drafts.csswg.org/css-extensions-1/#at-ruledef-custom-selector",
      "descriptors": [],
      "value": "@custom-selector <custom-selector> <selector-list> ;"
    }
  ],
  "selectors": [],
  "values": [
    {
      "name": "<extension-name>",
      "prose": "All extensions defined in this specification use a common syntax for defining their ”names”: the <extension-name> production. An <extension-name> is any identifier that starts with two dashes (U+002D HYPHEN-MINUS), like --foo, or even exotic names like -- or ------. The CSS language will never use identifiers of this form for any language-defined purpose, so it’s safe to use them for author-defined purposes without ever having to worry about colliding with CSS-defined names.",
      "href": "https://drafts.csswg.org/css-extensions-1/#typedef-extension-name",
      "type": "type"
    },
    {
      "name": "<custom-selector>",
      "href": "https://drafts.csswg.org/css-extensions-1/#typedef-custom-selector",
      "type": "type",
      "value": "<custom-arg>? : <extension-name> [ ( <custom-arg>+#? ) ]? ;"
    },
    {
      "name": "<custom-arg>",
      "href": "https://drafts.csswg.org/css-extensions-1/#typedef-custom-arg",
      "type": "type",
      "value": "$ <ident-token> ;"
    }
  ]
}