From:  http://www.nag.co.uk/projects/OpenMath/omstd/omobj.dtd
Date:  1999-05-20

<!-- DTD for OM Objects - sb 29.10.98 -->
<!-- sb 3.2.99 -->

<!--
     general list of embeddable elements
      : excludes OMATP as this is only embeddable in OMATTR
      : excludes OMBVAR as this is only embeddable in OMBIND
-->

<!ENTITY % omel "OMS | OMV | OMI | OMB | OMSTR
                                | OMF | OMA | OMBIND | OME
                                | OMATTR ">

<!-- things which can be variables -->

<!ENTITY % omvar "OMV | OMATTR" >

<!-- symbol -->
<!ELEMENT OMS EMPTY>
<!ATTLIST OMS name CDATA #REQUIRED
                          cd CDATA #REQUIRED >

<!-- variable -->
<!ELEMENT OMV EMPTY>
<!ATTLIST OMV name CDATA #REQUIRED >

<!-- integer -->
<!ELEMENT OMI (#PCDATA) >

<!-- byte array -->
<!ELEMENT OMB (#PCDATA) >

<!-- string -->
<!ELEMENT OMSTR (#PCDATA) >

<!-- floating point -->
<!ELEMENT OMF EMPTY>
<!ATTLIST OMF dec CDATA #IMPLIED
                          hex CDATA #IMPLIED>

<!-- apply constructor -->
<!ELEMENT OMA (%omel;)+ >

<!-- binding constructor & variable -->
<!ELEMENT OMBIND ((%omel;), OMBVAR, (%omel;)) >
<!ELEMENT OMBVAR (%omvar;)+ >

<!-- error -->
<!ELEMENT OME (OMS, (%omel;)* ) >

<!-- attribution constructor & attribute pair constructor -->
<!ELEMENT OMATTR (OMATP, (%omel;)) >
<!ELEMENT OMATP (OMS, (%omel;))+ >

<!-- OM object constructor -->
<!ELEMENT OMOBJ (%omel;) >