src/vs/workbench/browser/parts/editor/editorCommands.ts/registerSplitEditorCommands
function registerSplitEditorCommands() {
	[
		{ id: SPLIT_EDITOR_UP, direction: GroupDirection.UP },
		{ id: SPLIT_EDITOR_DOWN, direction: GroupDirection.DOWN },
		{ id: SPLIT_EDITOR_LEFT, direction: GroupDirection.LEFT },
		{ id: SPLIT_EDITOR_RIGHT, direction: GroupDirection.RIGHT }
	].forEach(({ id, direction }) => {
		CommandsRegistry.registerCommand(id, function (accessor, resourceOrContext?: URI | IEditorCommandsContext, context?: IEditorCommandsContext) {
			splitEditor(accessor.get(IEditorGroupsService), direction, getCommandsContext(resourceOrContext, context));
		});
	});
}