Source

File: wp-admin/includes/class-wp-posts-list-table.php

protected function is_base_request() {
		$vars = $_GET;
		unset( $vars['paged'] );

		if ( empty( $vars ) ) {
			return true;
		} elseif ( 1 === count( $vars ) && ! empty( $vars['post_type'] ) ) {
			return $this->screen->post_type === $vars['post_type'];
		}

		return 1 === count( $vars ) && ! empty( $vars['mode'] );
	}