src/vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/ast.ts/ListAstNode/flattenLists
class ListAstNode:	public flattenLists(): ListAstNode {
		const items: AstNode[] = [];
		for (const c of this.children) {
			const normalized = c.flattenLists();
			if (normalized.kind === AstNodeKind.List) {
				items.push(...normalized.children);
			} else {
				items.push(normalized);
			}
		}
		return ListAstNode.create(items);
	}