The <navref>  element represents a pointer to another map which is preserved
    as a transcluding link in the result deliverable rather than resolved when the deliverable is produced. Output formats that support such linking can integrate the referenced resource when displaying the referencing map to an end user. 
For example, if a map is converted to the Eclipse help system format, the DITA element
          <navref mapref="other.ditamap"/>
        is converted to the Eclipse element <link
          toc="other.xml"/>. When Eclipse loads the referencing map, it will replace
        this link element with the contents of the file other.xml, provided
        that the file other.xml is available.
Note that not all output formats support such linking. In order to include another map directly
    without depending on the output format, use a 
<topicref> element with the
     
@format attribute set to "ditamap". The effect is similar to using a
     
@conref attribute. For example, the following markup represents a literal
    inclusion of the map
    
other.ditamap:
<topicref href="other.ditamap" format="ditamap"/>
Content models
See appendix for information about this element in OASIS document type shells.
Example
In this example, the map titled "MyComponent tasks" references the maps
othermap2.ditamap and othermap3.ditamap.
<map title="MyComponent tasks">
 <navref mapref="../com.ibm.xml.doc/othermap1.ditamap"/>
 <navref mapref="../com.ibm.xml.doc/othermap2.ditamap"/>
</map>
Attributes
   The following attributes are available on this element: Universal attribute group, outputclass, @keyref, and the attribute
    defined below.
   
    
     - @mapref
- Specifies the URI of the map file or non-DITA resource to be referenced. It might reference a DITA map or a resource that is
            appropriate for your output format (such as XML TOC file for Eclipse output).
            
- @keyref(DEPRECATED)
- The @keyrefattribute was unintentionally defined for<navref>in the original DITA grammar files. It is retained for
      backwards compatibility. The attribute will be removed in a future release, and processors are
      not expected to support it.