2.1.14 [HTML] Section 11.2.3, Row groups: the THEAD, TFOOT, and TBODY elements
When present, each THEAD, TFOOT, and TBODY contains a row group. Each row group must contain at least one row, defined by the TR element.
Quirks Mode, IE7 Mode, IE8 Mode, and IE9 Mode (All Versions)
THEAD, TFOOT, and TBODY are not required to contain a row defined by the TR element.
The TBODY start tag is always required except when the table contains only one table body and no table head or foot sections.
All Document Modes (All Versions)
The TBODY start tag is always optional and will be implied for any TR elements that are direct children of a TABLE element.