Answer 1

An Html attribut of cell elements ( <td> ... ) to merge many cells in one on a row ( one cell through many spanned columns )... the value of the attribute is the number of cells from the one with the attribut included to merge. 'colspan' have his complementary 'rowspan' which handle cells on a column in equivalent way with spanned rows...
Implicitly merged cells need to not be included in html <table> structure, as they does no more exists since the content is the one of the cell with the attribute:
<style>
table { border-spacing:5px; border:2px solid: black; }
td { padding:10px; border:1px solid black; }
</style>
<table>
<tr>
<td rowspan="2"> cell 1 </td>
<td> cell 2 </td>
<td> cell 3 </td>
</tr>
<tr>
<!-- this is merged with cell 1
<td> cell A </td>
-->
<td colspan="2"> cell B </td>
<!-- this is merged with cell B
<td> cell C </td>
-->
</tr>
</table>