Tables with colspans or rowspans, so that there aren’t the same number of cells in each row or in each column, totally break sorttable. Is there a reasonable approach to take here?
It’s not clear precisely how to sort a table like this. Note also that this should cope with rowspans in the <thead>.
Some thoughts from Stephen Kitt:
The general idea for handling rowspans in the header is to only provide
the sorting hooks on the last row in a column; so the code loops over
the rows in the header, and processes cells whose rowspan extends them
all the way to the bottom of the header. The sorttable_columnindex is
updated according to the colspan of each processed cell.