If you run WP website and installed whatever plugin which should make sitemap.xml for WP (Yoast, All in one SEO, Google sitemaps, …) sometimes you might bump on this error message when trying to open and see your sitemap:
error on line 7 at column 6: XML declaration allowed only at the start of the document
You might loose much time searching for incorrect php file in your theme, plugins or core WP files.
Continue reading Error on line 7 at column 6: XML declaration allowed only at the start of the document