Used for any kind of internal referencing
This element may be used to reference anything that has an id attribute (an attribute of type id). This single element takes the place of the many named types of references (such as figure references, table references, and footnote references) that are common in many DTDs.
Unlike the base DTD Suite, the NCBI Book DTD’s and the NCBI Collection DTD’s content model for this element includes graphical elements for use in instances where, for example, an onscreen arrow serves as the link to a picture or database.
Display/Formatting Note: The content of the reference (if present) will be displayed as the link.
<!ELEMENT xref (#PCDATA %xref-elements;)* >
Any combination of:
<aff> Affiliation; <alt-title> Alternate Title; <article-title> Article Title; <attrib> Attribution; <bold> Bold; <book-title> Book Title; <chem-struct> Chemical Structure (Display); <collab> Collaborative (Group) Author; <collection-name> Collection Name; <comment> Comment in a Citation; <contrib> Contributor; <contrib-group> Contributor Group; <def-head> Definition List: Definition Head; <italic> Italic; <kwd> Keyword; <meta-name> Metadata Data Name for Custom Metadata; <meta-value> Metadata Data Value for Custom Metadata; <monospace> Monospace Text (Typewriter Text); <multi-link> Multi-Link; <named-content> Named Special (Subject) Content; <overline> Overline; <p> Paragraph; <sc> Small Caps; <speaker> Speaker; <strike> Strike Through; <sub> Subscript; <subtitle> Subtitle; <sup> Superscript; <td> Table Data Cell (XHTML table model); <term> Definition List: Term; <term-head> Definition List: Term Head; <th> Table Header Cell (XHTML table model); <title> Title; <trans-subtitle> Translated Subtitle; <trans-title> Translated Title; <underline> Underline
... <sec id="bid.36"> <title>Microbial Genomes</title> <p>... A CON entry, containing instructions on how to put the pieces back together, is also made. The CON entry contains descriptor information, such as source organism and references, as well as a join statement providing explicit instructions on how to generate the complete genome from the pieces. The Accession number assigned to the CON record is also added as a secondary Accession number on each of the pieces that make up the complete genome (see <xref ref-type="fig" rid="bid.37">Figure 2</xref>). <fig id="bid.37"> <label>2</label> <caption><title>A GenBank CON entry for a complete bacterial genome.</title> <p>The information toward the <italic>bottom</italic> of the record describes how to generate the complete genome from the pieces.</p> </caption> <graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ch1f2" mime-subtype="gif"/> </fig> </p> ... </sec> ...