Cross nesting between A, BUTTON, SELECT and TEXTAREA is forbidden:<br>
<dl>
<dt>A:
 <dd> A A<a><a></a>
 <dd> A BUTTON<a><button value="OK" name="sop"></button></a>
 <dd> A SELECT<a><select></select></a>
 <dd> A TEXTAREA<a><textarea rows=1 cols=1></textarea></a>
<dt>BUTTON:
 <dd> BUTTON A<button><a></button>
 <dd> BUTTON BUTTON<button><button value="OK" name="sop"></button></button>
 <dd> BUTTON SELECT<button><select></button>>
 <dd> BUTTON TEXTAREA<button><textarea rows=1 cols=1></textarea></button>
<dt>SELECT:
 <dd> SELECT A<select><a></select>
 <dd> SELECT BUTTON<select><button value="OK" name="sop"></button></select>
 <dd> SELECT SELECT<select><select></select>>
 <dd> SELECT TEXTAREA<select><textarea rows=1 cols=1></textarea></select>
<dt>TEXTAREA:
 <dd> TEXTAREA A<textarea><a></a></textarea>
 <dd> TEXTAREA BUTTON<textarea><button value="OK"></button></textarea>
 <dd> TEXTAREA SELECT<textarea><select></select></textarea>>
 <dd> TEXTAREA TEXTAREA<textarea><textarea rows=1 cols=1></textarea></textarea>

</dl>