Validator gives table errors - html

Question

I have to make a table like
and I have this code so far:
table, td, tr {
border: 1px solid black;
}
td {
width: 50px;
height: 50px;
}
td[rowspan="2"] {
height: 100px;
}
td[colspan="2"] {
width: 100px;
}
<div>
<table>
<tr>
<td>a</td>
<td colspan="2">b</td>
</tr>
<tr>
<td rowspan="2">c</td>
<td colspan="2" rowspan="2">
<table>
<tr>
<td colspan="2" rowspan="2">d</td>
</tr>
<tr></tr>
</table>
</td>
</tr>
<tr></tr>
</table>
</div>
The validator is giving me
and I don't know how to fix them.
I need no errors from the validator, as
it has to be acceptable by specification.

Answer 1

rowspans and colspans are only used if a cell should span 2 other cells horizontally or vertically, which isn't the case in your example. They are not there to define width or height.
So delete those and use classes instead to define the properties you want:
Apart from that, delete those empty tr elements you have in there - they make no sense without tds in them. ALso the nested table with only one cell in it is rather strange (you could just fill that cell with content), but maybe there's a reason for that which you didn't tell us.
table, td, tr {
border: 1px solid black;
}
td {
width: 50px;
height: 50px;
}
td.b {
height: 100px;
}
td.a {
width: 100px;
}
<div>
<table>
<tr>
<td>a</td>
<td class="a">b</td>
</tr>
<tr>
<td class="b">c</td>
<td class="a b" >
<table>
<tr>
<td class="a b">d</td>
</tr>
</table>
</td>
</tr>
</table>
</div>