Use W3C documentation for the XHTML1.1 table model. (http://www.w3.org/TR/xhtml-modularization/abstract_modules.html#s_tablemodule)
Groups several attributes that affect vertical alignment, for use in the attribute lists of several elements.
<!ENTITY % CellVAlign.attrib "valign ( top | middle | bottom | baseline ) #IMPLIED" >
JATS-xhtml-table-1.mod