Method markPureFromAtRulePrelude

lib/css/CssParser.js:3066–3099

(
			at,
			isKeyframes,
			isCounterStyle,
			isContainer
		)

		 * @returns {void}
		 */
		const markPureFromAtRulePrelude = (
			at,
			isKeyframes,
			isCounterStyle,
			isContainer
		) => {
			const acceptIdent = isKeyframes || isCounterStyle || isContainer;
			const acceptString = isKeyframes;
			for (const cv of A.prelude(at)) {
				const cvType = A.type(cv);
				if (cvType === NodeType.Whitespace) continue;
				if (cvType === NodeType.String) {
					if (acceptString) pure.markLocal();
					break;
				}
				if (cvType === NodeType.Ident) {
					if (!acceptIdent) break;
					if (
						isContainer &&
						isContainerKeyword(source, A.start(cv), A.end(cv))
					) {
						continue;
					}
					pure.markLocal();
					break;
				}
				if (cvType === NodeType.Function) {
					if (equalsLowerCase(A.unescapedName(cv), "local")) {
						pure.markLocal();
					}
					break;
				}
			}
		};

		// Drive the walk through SourceProcessor: structural enter / exit map to the `walkAst…Enter` / `…Exit` halves; value visitors handle url / ICSS / local-global.
		/** @type {VisitorMap} */