The attribute gml:id supports provision of a handle for the XML element representing a GML Object. Its use is mandatory for all GML objects. It is of XML type ID, so is constrained to be unique in the XML document within which it occurs.
<complexType name="GenericMetaDataType" mixed="true"> <annotation> <appinfo>deprecated</appinfo> </annotation> <complexContent mixed="true"> <extension base="gml:AbstractMetaDataType"> <sequence> <any processContents="lax" minOccurs="0" maxOccurs="unbounded"/> </sequence> </extension> </complexContent> </complexType>