src/vs/workbench/services/workingCopy/common/workingCopyEditorService.ts/WorkingCopyEditorService/registerHandler
class WorkingCopyEditorService:	registerHandler(handler: IWorkingCopyEditorHandler): IDisposable {

		// Add to registry and emit as event
		this.handlers.add(handler);
		this._onDidRegisterHandler.fire(handler);

		return toDisposable(() => this.handlers.delete(handler));
	}