--- build_tools/make_xml_documentation.orig	2022-06-23 15:26:13 UTC
+++ build_tools/make_xml_documentation
@@ -214,7 +214,7 @@ for subdir in ${mod_subdirs} ; do
 					${XMLSTARLET} val -e -d "${source_tree}/doc/appdocsxml.dtd" "${i}" || { echo "" ; exit 1 ; }
 			fi
 		fi
-		${SED} -r "/^\s*(<[?]xml|<.DOCTYPE|<.?docs)/d" "${i}" >> "${output_file}"
+		${SED} -r "/^[[:space:]]*(<[?]xml|<.DOCTYPE|<.?docs)/d" "${i}" >> "${output_file}"
 	done
 done
 echo "</docs>" >> "${output_file}"