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