First cell of the main table can not even contain a table
col1 col2

The table with [col1]-[col2] cells should appear in the second cell above this text (see browsers, MS Word), but in the LibreOffice Writer unexpectedly moves into the first cell if the first entity in the cell is the table tag. If any non-whitespace text or any other tag (like p) appear before the table tag, this works as a workaround for this issue