Requirements for the Use of the Object (en)
* OpenGIS® Geography Markup Language Encoding Standard (GML): {link}http://www.opengeospatial.org/standards/gml{/link}
* version 3.2.1
* file extension: .gml
* Extended from XML: {link}https://www.w3.org/TR/REC-xml/{/link}
* Standard: {link}http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=32554{/link}