W3C validator: “Element head is missing a required instance of child element title”

问题

I'm trying to validate my document for HTML5 using the W3C validator at http://validator.w3.org/check. When I run the code below using "direct input" I get error messages like Element head is missing a required instance of child element title and Stray start tag html. This baffles me, because the <html> tag is right there. Why can't the validator see it?

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<meta name="description" content="some content">
<title>page title</title>
</head>
<body>
</body>
</html>

Update: I'm using PHP to generate parts of the file and it turns out this was the cause of the error.

回答1:

I discovered the error. I'm using PHP to generate the page. When I viewed it in a hex editor I discovered two null bytes (hex code 0x00) before the tag. Exactly where my first <?php ?> tag were. When I copied the code or ran it by URL, the validator encountered the null bytes. When I wrote the code manually, it validated fine.

<!DOCTYPE html>
<?php
/* the PHP tag apparently outputs two null bytes */
?>
<html>
<head>
<title>page title</title>
</head>
<body>page body</body>
</html>

I moved the first PHP tag down to the first line of the body and the validation passed.