src/vs/workbench/browser/parts/editor/tabsTitleControl.ts/TabsTitleControl/isSupportedDropTransfer
class TabsTitleControl:	private isSupportedDropTransfer(e: DragEvent): boolean {
		if (this.groupTransfer.hasData(DraggedEditorGroupIdentifier.prototype)) {
			const data = this.groupTransfer.getData(DraggedEditorGroupIdentifier.prototype);
			if (Array.isArray(data)) {
				const group = data[0];
				if (group.identifier === this.group.id) {
					return false; // groups cannot be dropped on title area it originates from
				}
			}

			return true;
		}

		if (this.editorTransfer.hasData(DraggedEditorIdentifier.prototype)) {
			return true; // (local) editors can always be dropped
		}

		if (e.dataTransfer && e.dataTransfer.types.length > 0) {
			return true; // optimistically allow external data (// see https://github.com/microsoft/vscode/issues/25789)
		}

		return false;
	}