gml:AbstractGML 

The abstract element gml:AbstractGML is "any GML object having identity".   It acts as the head of an XML Schema substitution group, which may include any element which is a GML feature, or other object, with identity.  This is used as a variable in content models in GML core and application schemas.  It is effectively an abstract superclass for all GML objects.

Element Information

Model

gml:metaDataProperty* , gml:description{0,1} , gml:descriptionReference{0,1} , gml:identifier{0,1} , gml:name*
Children: gml:description, gml:descriptionReference, gml:identifier, gml:metaDataProperty, gml:name

Attributes

QName Type Fixed Default Use Inheritable Annotation
gml:id ID required 
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.

Source 

<element name="AbstractGML" type="gml:AbstractGMLType" abstract="true" substitutionGroup="gml:AbstractObject">
  <annotation>
    <documentation>The abstract element gml:AbstractGML is "any GML object having identity". It acts as the head of an XML Schema substitution group, which may include any element which is a GML feature, or other object, with identity. This is used as a variable in content models in GML core and application schemas. It is effectively an abstract superclass for all GML objects.</documentation>
  </annotation>
</element>

Sample