src/vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/ast.ts/TwoThreeListAstNode/prependChildOfSameHeight
class TwoThreeListAstNode:	public prependChildOfSameHeight(node: AstNode): void {
		if (this._item3) {
			throw new Error('Cannot prepend to a full (2,3) tree node');
		}
		this.throwIfImmutable();
		this._item3 = this._item2;
		this._item2 = this._item1;
		this._item1 = node;
		this.handleChildrenChanged();
	}