<schemeref>
  
A scheme reference is the mechanism for referencing a subject scheme map.
Specialization hierarchy
The <schemeref> element is specialized from
          <topicref>. It is defined in the subject scheme module.
Content model
<topicmeta>?, <data>**
Contained by
- Optional 
<topicmeta> - Zero or more Zero or more 
<data> 
Contained by
Inheritance
- map/topicref subjectScheme/schemeref
The <schemeref> element is specialized from <topicref>. It is defined in the subjectScheme module.
Attributes
The following attributes are available on this element: link-relationship attributes, universal
                                                  attributes, @impose-role, @keyref, and @keys.
- The 
@formatattribute has a default value of ditamap. - The 
@impose-roleattribute has a fixed value of keeptarget. - The 
@typeattribute has a default value of scheme. 
The following attributes are available on this element: universal attributes and the attributes defined below.
@format(link-relationship attributes)- Specifies the format of the resource that is referenced. See The format attribute for detailed information on supported values and processing implications.
 @href(link-relationship attributes)- Specifies a reference to a resource. See The href attribute for detailed information on supported values and processing implications.
 @impose-role- Specifies whether this element will impose its role on elements in a referenced map.
            The attribute is ignored if the target of the reference is not a map or branch of a map.
            The following values are valid: 
- keeptarget
 - The role of the current reference is not imposed on the target of the reference.
                  This is the default for the unspecialized 
<topicref>element and for many convenience elements such as<keydef>. - impose
 - The role of the current reference is imposed on the target of the reference. For example, if a specialized topic reference
                      
<chapter>uses this value and references a map, a topic reference that resolves in place of the<chapter>will be treated as if it were a chapter. - -dita-use-conref-target
 - See Using the -dita-use-conref-target value for more information.
 
See The href attribute for detailed information on supported values and processing implications.
 @keyref- Specifies a key name that acts as a redirectable reference based on a key definition within a map. See The keyref attribute for information on using this attribute.
 @keys- Specifies one or more names for a resource. See Setting key names with the keys attribute for information on using this attribute.
 @scope(link-relationship attributes)- Specifies the closeness of the relationship between the
            current document and the referenced resource. The following values are valid:
                local, peer,
                external, and
                -dita-use-conref-target. 
See The scope attribute for detailed information on supported values and processing implications.
 @type(link-relationship attributes)- Describes the target of a reference. See The type attribute for detailed information on supported values and processing implications.