This is the Relax NG Schema described in Section 3.1 expressed according to the Relax NG XML Syntax.
<grammar
xmlns="http://relaxng.org/ns/structure/1.0" ns="http://www.openmath.org/OpenMath" datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
<start>
<ref name="OMOBJ"/>
</start>
<!-- OpenMath object constructor -->
<define name="OMOBJ">
<element name="OMOBJ">
<ref name="compound.attributes"/>
<optional>
<attribute name="version">
<data type="string"/>
</attribute>
</optional>
<ref name="omel"/>
</element>
</define>
<!-- Elements which can appear inside an OpenMath object -->
<define name="omel">
<choice>
<ref name="OMS"/>
<ref name="OMV"/>
<ref name="OMI"/>
<ref name="OMB"/>
<ref name="OMSTR"/>
<ref name="OMF"/>
<ref name="OMA"/>
<ref name="OMBIND"/>
<ref name="OME"/>
<ref name="OMATTR"/>
<ref name="OMR"/>
</choice>
</define>
<!-- things which can be variables -->
<define name="omvar">
<choice>
<ref name="OMV"/>
<ref name="attvar"/>
</choice>
</define>
<define name="attvar">
<element name="OMATTR">
<ref name="common.attributes"/>
<group>
<ref name="OMATP"/>
<choice>
<ref name="OMV"/>
<ref name="attvar"/>
</choice>
</group>
</element>
</define>
<define name="cdbase">
<optional>
<attribute name="cdbase">
<data type="anyURI"/>
</attribute>
</optional>
</define>
<!-- attributes common to all elements -->
<define name="common.attributes">
<optional>
<attribute name="id">
<data type="ID"/>
</attribute>
</optional>
</define>
<!-- attributes common to all elements that construct compount OM objects. -->
<define name="compound.attributes">
<ref name="common.attributes"/>
<ref name="cdbase"/>
</define>
<!-- symbol -->
<define name="OMS">
<element name="OMS">
<ref name="common.attributes"/>
<attribute name="name">
<data type="NCName"/>
</attribute>
<attribute name="cd">
<data type="NCName"/>
</attribute>
<ref name="cdbase"/>
</element>
</define>
<!-- variable -->
<define name="OMV">
<element name="OMV">
<ref name="common.attributes"/>
<attribute name="name">
<data type="NCName"/>
</attribute>
</element>
</define>
<!-- integer -->
<define name="OMI">
<element name="OMI">
<ref name="common.attributes"/>
<data type="string">
<param name="pattern">\s*(-\s?)?[0-9]+(\s[0-9]+)*\s*</param>
</data>
</element>
</define>
<!-- byte array -->
<define name="OMB">
<element name="OMB">
<ref name="common.attributes"/>
<data type="base64Binary"/>
</element>
</define>
<!-- string -->
<define name="OMSTR">
<element name="OMSTR">
<ref name="common.attributes"/>
<text/>
</element>
</define>
<!-- IEEE floating point number -->
<define name="OMF">
<element name="OMF">
<ref name="common.attributes"/>
<choice>
<attribute name="dec">
<data type="double"/>
</attribute>
<attribute name="hex">
<data type="string">
<param name="pattern">[0-9A-F]+</param>
</data>
</attribute>
</choice>
</element>
</define>
<!-- apply constructor -->
<define name="OMA">
<element name="OMA">
<ref name="compound.attributes"/>
<oneOrMore>
<ref name="omel"/>
</oneOrMore>
</element>
</define>
<!-- binding constructor -->
<define name="OMBIND">
<element name="OMBIND">
<ref name="compound.attributes"/>
<ref name="omel"/>
<ref name="OMBVAR"/>
<ref name="omel"/>
</element>
</define>
<!-- variables used in binding constructor -->
<define name="OMBVAR">
<element name="OMBVAR">
<ref name="common.attributes"/>
<oneOrMore>
<ref name="omvar"/>
</oneOrMore>
</element>
</define>
<!-- error constructor -->
<define name="OME">
<element name="OME">
<ref name="common.attributes"/>
<ref name="OMS"/>
<zeroOrMore>
<choice>
<ref name="omel"/>
<ref name="OMFOREIGN"/>
</choice>
</zeroOrMore>
</element>
</define>
<!-- attribution constructor and attribute pair constructor -->
<define name="OMATTR">
<element name="OMATTR">
<ref name="compound.attributes"/>
<ref name="OMATP"/>
<ref name="omel"/>
</element>
</define>
<define name="OMATP">
<element name="OMATP">
<ref name="compound.attributes"/>
<oneOrMore>
<ref name="OMS"/>
<choice>
<ref name="omel"/>
<ref name="OMFOREIGN"/>
</choice>
</oneOrMore>
</element>
</define>
<!-- foreign constructor -->
<define name="OMFOREIGN">
<element name="OMFOREIGN">
<ref name="compound.attributes"/>
<optional>
<attribute name="encoding">
<data type="string"/>
</attribute>
</optional>
<zeroOrMore>
<choice>
<ref name="omel"/>
<ref name="notom"/>
</choice>
</zeroOrMore>
</element>
</define>
<!--
Any elements not in the om namespace
(valid om is allowed as a descendant)
-->
<define name="notom">
<choice>
<element>
<anyName>
<except>
<nsName/>
</except>
</anyName>
<zeroOrMore>
<attribute>
<anyName/>
</attribute>
</zeroOrMore>
<zeroOrMore>
<choice>
<ref name="omel"/>
<ref name="notom"/>
</choice>
</zeroOrMore>
</element>
<text/>
</choice>
</define>
<!-- reference constructor -->
<define name="OMR">
<element name="OMR">
<ref name="common.attributes"/>
<attribute name="href">
<data type="anyURI"/>
</attribute>
</element>
</define>
</grammar>