%thead.content; Table Header Element (thead) Content
Defines what elements can occur within the <thead> element in NISO JATS tables.
The NISO JATS table model parameter entity is used in the same way as the equivalent parameter entity in the XHTML 1.1 table model. Since this parameter entity was named in the same way as the XHTML 1.1 Tag Set equivalent, it does not follow the naming conventions for this Tag Set: it is in mixed (not lower) case, and the separator character is a period, not a hyphen.
<!ENTITY % thead.content "( %tr.qname; )+" >
( tr )+