Table nested 3 levels, table3 be the out most.
<br> Table 1 is not in table2's tr-td. That makes table2 invalid.
<br>Table3 is still valid, and table2's tr and td are used for
table3.

<table border>
<caption> caption of table3.</caption>
<tr>
<td>
  <table border>
  <caption> caption of table2.</caption>
  Text after table2, not in tr-td, but in table3's tr-td.
    <table border>
    <caption> caption of table1.</caption>
    <tr>
    <td>first cell in table1
    <td>second cell in table1
    <tr>
    <td>third cell in the table1
    <td>fourth cell in the table1
    </table>
  <tr>
  <td>first cell in table2, but displayed in table 3.
  </table>
<td>
  second cell in table3. but table2's end tag closed table3.
  So, this will be displayed out of table3.
</table>