You can answer your own question. View the source of your
resulting rendered page. How many times does
<head>...</head> show up where it shouldn't be (namely,
after the opening <html> tag and before the opening
<body> tag). Any <head>...</head> tags that are
inside the <body> tag are invalid HTML according to spec, and
most definitely invalid XHTML, even Transitional XHTML. The
(trimmed, necessary elements only, without attribute declarations)
DTD you specify in your DOCTYPE declaration specifies:
<!ELEMENT html (head, body)>
<!ENTITY % head.misc
"(script|style|meta|link|object|isindex)*">
<!ELEMENT head (%head.misc;,
((title, %head.misc;, (base, %head.misc;)?) |
(base, %head.misc;, (title, %head.misc;))))>
<!ELEMENT body %Flow;>
<!-- %Flow; mixes block and inline and is used for list
items etc. -->
<!ENTITY % Flow "(#PCDATA | %block; | form | %inline; |
%misc;)*">
<!ENTITY % block
"p | %heading; | div | %lists; | %blocktext; | isindex
|fieldset | table">
<!ENTITY % heading "h1|h2|h3|h4|h5|h6">
<!ENTITY % lists "ul | ol | dl | menu | dir">
<!ENTITY % blocktext "pre | hr | blockquote | address |
center | noframes">
<!ENTITY % inline "a | %special; | %fontstyle; | %phrase;
| %inline.forms;">
<!ENTITY % special.extra
"object | applet | img | map | iframe">
<!ENTITY % special.basic
"br | span | bdo">
<!ENTITY % special
"%special.basic; | %special.extra;">
<!ENTITY % fontstyle.extra "big | small | font |
basefont">
<!ENTITY % fontstyle.basic "tt | i | b | u
| s | strike ">
<!ENTITY % fontstyle "%fontstyle.basic; |
%fontstyle.extra;">
<!ENTITY % phrase.extra "sub | sup">
<!ENTITY % phrase.basic "em | strong | dfn | code | q |
samp | kbd | var | cite | abbr | acronym">
<!ENTITY % phrase "%phrase.basic; | %phrase.extra;">
<!ENTITY % inline.forms "input | select | textarea | label
| button">
<!-- these can occur at block or inline level -->
<!ENTITY % misc.inline "ins | del | script">
<!-- these can only occur at block level -->
<!ENTITY % misc "noscript | %misc.inline;">
Meaning a valid XHTML-transitional document consists of, at
minimum:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
Transitional//EN" "
http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="
http://www.w3.org/1999/xhtml">
<head>
</head>
<body>
</body>
</html>
But nowhere inside the body tag can you have another head or
body tag. So, short answer, you shouldn't HAVE a header
(<head>...</head>) in your subpages (unless, as Dan
says, they're being rendered in frames, in which case they have to
be complete, valid pages on their own).