# Declaration merging is not supported Rule ``arkts-no-decl-merging`` **Severity: error** ArkTS does not support merging declarations. Keep all definitions of classes and interfaces compact in the codebase. ## TypeScript ``` interface Document { createElement(tagName: any): Element } interface Document { createElement(tagName: string): HTMLElement } interface Document { createElement(tagName: number): HTMLDivElement createElement(tagName: boolean): HTMLSpanElement createElement(tagName: string, value: number): HTMLCanvasElement } ``` ## ArkTS ``` interface Document { createElement(tagName: number): HTMLDivElement createElement(tagName: boolean): HTMLSpanElement createElement(tagName: string, value: number): HTMLCanvasElement createElement(tagName: string): HTMLElement createElement(tagName: Object): Element } ```