Example.
<TABLE border="1">
<TR>
<TD> </TD>
<TH id="meals">Meals</TH>
<TH id="hotels">Hotels</TH>
<TH id="transport">Transport</TH>
<TH id="triptotals">Trip Totals</TH>
</TR>
<TR>
<TH colspan="5" id="san_jose">San Jose</TH>
</TR>
<TR>
<TD id="aug-25-97" headers="san_jose">25-Aug-97</TD>
<TD headers="san_jose aug-25-97 meals">37.74</TD>
<TD headers="san_jose aug-25-97 hotels">112.00</TD>
<TD headers="san_jose aug-25-97 transport">45.00</TD>
<TD> </TD>
</TR>
<TR>
<TD id="aug-26-97" headers="san_jose">26-Aug-97</TD>
<TD headers="san_jose aug-26-97 meals">27.28</TD>
<TD headers="san_jose aug-26-97 hotels">112.00</TD>
<TD headers="san_jose aug-26-97 transport">45.00 </TD>
<TD> </TD>
</TR>
<TR>
<TH id="sub" headers="san_jose">Subtotals </TH>
<TD headers="san_jose sub meals">65.02</TD>
<TD headers="san_jose sub hotels">224.00</TD>
<TD headers="san_jose sub transport">90.00</TD>
<TD headers="san_jose triptotals">379.02</TD>
</TR>
<TR>
<TH colspan="5" id="Seattle">Seattle</TH>
</TR>
<TR>
<TD id="aug-27-97" headers="Seattle">27-Aug-97</TD>
<TD headers="Seattle aug-27-97 meals">96.25</TD>
<TD headers="Seattle aug-27-97 hotels">109.00</TD>
<TD headers="Seattle aug-27-97 transport">36.00</TD>
<TD> </TD>
</TR>
<TR>
<TD id="aug-28-97" headers="Seattle">28-Aug-97</TD>
<TD headers="Seattle aug-28-97 meals">35.00</TD>
<TD headers="Seattle aug-28-97 hotels">109.00</TD>
<TD headers="Seattle aug-28-97 transport">36.00 </TD>
<TD> </TD>
</TR>
<TR>
<TH is="sub2" headers="Seattle">subtotals</TH>
<TD headers="Seattle sub meals">131.25</TD>
<TD headers="Seattle sub hotels">218.00</TD>
<TD headers="Seattle sub transport">72.00</TD>
<TD headers="Seattle triptotals">421.25</TD>
</TR>
<TR>
<TH id="grandtotals">Totals</TH>
<TD headers="grandtotals meals">196.27</TD>
<TD headers="grandtotals hotels">442.00</TD>
<TD headers="grandtotals transport">162.00</TD>
<TD headers="grandtotals triptotals">800.27</TD>
</TR>
</TABLE>
End example.
Note: this table example taken from the US Department of Energy, Energy Efficiency and Renewable Energy (EERE) Communication Standards and Guidleines. View the original EERE page.