Captions in union table model

["David M. Jones" <dmj@ams.org>]

Greetings,

Is the caption element really meant to be required in the union table
content model in htmltblx.mod?

    <!-- DocBook XML HTML Table Module V4.4b2 ................................... -->
    
    [...]
    
    <!-- Content model for Table (that also allows HTML tables) -->
    <!ENTITY % tbl.table.mdl
    	"((blockinfo?,
               (%formalobject.title.content;),
               (%ndxterm.class;)*,
               textobject*,
               (graphic+|mediaobject+|tgroup+))
             |(caption, (col*|colgroup*), thead?, tfoot?, (tbody+|tr+)))">

My apologies if this is an FAQ.  I poked around the list archives but
couldn't find any discussion of this.

Cheers,
David.