Hard to understand XHTML validation errors

In the following, please use lowercase tags (uppercase used for clarity)

• No DIV allowed in A
  do not write <A><DIV>Hello</DIV></A>
  write instead <A><SPAN>Hello</SPAN></A>
• No INPUT allowed in FORM
  do not write <FORM><INPUT /></FORM>
  write instead <FORM><DIV><INPUT /></DIV></FORM>