NCBI element citation

Abstract	false (This can be used in an instance)
Nillable	false (Instance values cannot use xsi:nil)
Declared Namespaces	xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance xmlns:xlink=http://www.w3.org/1999/xlink xmlns:xs=http://www.w3.org/2001/XMLSchema xmlns:mml=http://www.w3.org/1998/Math/MathML

<xs:element name="citation">
    <xs:complexType mixed="true">
        <xs:choice minOccurs="0" maxOccurs="unbounded">
            <xs:element ref="bold"/>
            <xs:element ref="italic"/>
            <xs:element ref="monospace"/>
            <xs:element ref="overline"/>
            <xs:element ref="sc"/>
            <xs:element ref="strike"/>
            <xs:element ref="underline"/>
            <xs:element ref="inline-graphic"/>
            <xs:element ref="private-char"/>
            <xs:element ref="inline-formula"/>
            <xs:element ref="label"/>
            <xs:element ref="abbrev"/>
            <xs:element ref="named-content"/>
            <xs:element ref="access-date"/>
            <xs:element ref="annotation"/>
            <xs:element ref="article-title"/>
            <xs:element ref="collab"/>
            <xs:element ref="comment"/>
            <xs:element ref="conf-date"/>
            <xs:element ref="conf-loc"/>
            <xs:element ref="conf-name"/>
            <xs:element ref="day"/>
            <xs:element ref="edition"/>
            <xs:element ref="email"/>
            <xs:element ref="elocation-id"/>
            <xs:element ref="etal"/>
            <xs:element ref="ext-link"/>
            <xs:element ref="fpage"/>
            <xs:element ref="gov"/>
            <xs:element ref="isbn"/>
            <xs:element ref="issn"/>
            <xs:element ref="issue"/>
            <xs:element ref="issue-id"/>
            <xs:element ref="issue-title"/>
            <xs:element ref="lpage"/>
            <xs:element ref="month"/>
            <xs:element ref="name"/>
            <xs:element ref="object-id"/>
            <xs:element ref="page-count"/>
            <xs:element ref="page-range"/>
            <xs:element ref="patent"/>
            <xs:element ref="person-group"/>
            <xs:element ref="pub-id"/>
            <xs:element ref="publisher-loc"/>
            <xs:element ref="publisher-name"/>
            <xs:element ref="role"/>
            <xs:element ref="season"/>
            <xs:element ref="series"/>
            <xs:element ref="source"/>
            <xs:element ref="std"/>
            <xs:element ref="supplement"/>
            <xs:element ref="time-stamp"/>
            <xs:element ref="trans-source"/>
            <xs:element ref="trans-title"/>
            <xs:element ref="uri"/>
            <xs:element ref="volume"/>
            <xs:element ref="volume-id"/>
            <xs:element ref="year"/>
            <xs:element ref="sub"/>
            <xs:element ref="sup"/>
        </xs:choice>
        <xs:attribute name="citation-type">
            <xs:simpleType>
                <xs:restriction base="xs:token">
                    <xs:enumeration value="book"/>
                    <xs:enumeration value="commun"/>
                    <xs:enumeration value="confproc"/>
                    <xs:enumeration value="discussion"/>
                    <xs:enumeration value="gov"/>
                    <xs:enumeration value="journal"/>
                    <xs:enumeration value="list"/>
                    <xs:enumeration value="patent"/>
                    <xs:enumeration value="thesis"/>
                    <xs:enumeration value="web"/>
                    <xs:enumeration value="other"/>
                </xs:restriction>
            </xs:simpleType>
        </xs:attribute>
        <xs:attribute name="id" type="xs:ID"/>
        <xs:attribute ref="xlink:type"/>
        <xs:attribute ref="xlink:href"/>
        <xs:attribute ref="xlink:role"/>
        <xs:attribute ref="xlink:title"/>
        <xs:attribute ref="xlink:show"/>
        <xs:attribute ref="xlink:actuate"/>
    </xs:complexType>
</xs:element>

element {}citation

Source