Ho provato a fare la validazione della mia pagina e ho ricevuto questi errori:

1)

Error Line 21, Column 3: "DOCTYPE" declaration not allowed in instance

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/…


2)

Error Line 23, Column 67: document type does not allow element "html" here

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">

3)

Error Line 134, Column 69: required attribute "action" not specified

<form id="register" method="post" onsubmit="return validazione()">

4)

Error Line 151, Column 40: end tag for "select" which is not finished

<td> <select id="giorno"></select>

5)

Error Line 152, Column 63: end tag for "select" which is not finished

<select id="mese" onchange="controllaData()"></select>


6)

Error Line 153, Column 63: end tag for "select" which is not finished

<select id="anno" onchange="controllaData()"></select>


chi mi li puo spiegare il motivo di questi errori?