This page gives an overview of issues that occur in the XML and should be avoided
Many XML processing applications (such as our Highwire Online platforms) do not process XML with the BOM Marker in place. Files including a BOM marker cannot be loaded. Existence of the marker should be avoided. XML-editors offer different options for avoiding the BOM-marker in the output. in Oxygen for example it is possible to set the in Preferences->"Encoding" the "UTF-8 BOM handling" to "Don't Write". In case of a file with a BOM-marker, the file should be saved again after making this change in the Preferences.