What is needed for a valid WXR file?

I’m creating a WXR from scratch that later will be imported into WordPress. I′m converting from an older system and need to know what is needed and what is optional? Is there any docs. on this?

The head section I can take from current WP setup but what about the item section. Here is an example of an item:

<item>
<title>AIK hockey</title>
<pubDate>Thu, 25 Feb 2010 16:37:19 +0000</pubDate>
<dc:creator><![CDATA[jenswedin]]></dc:creator>

		<category><![CDATA[Team Sweden]]></category>
		<category domain="category" nicename="team-sweden"><![CDATA[Team Sweden]]></category>

<description></description>
<content:encoded><![CDATA[]]></content:encoded>
<excerpt:encoded><![CDATA[]]></excerpt:encoded>
<wp:post_id></wp:post_id>
<wp:post_date></wp:post_date>
<wp:post_date_gmt></wp:post_date_gmt>
<wp:comment_status>open</wp:comment_status>
<wp:ping_status>open</wp:ping_status>
<wp:post_name></wp:post_name>
<wp:status>draft</wp:status>
<wp:post_parent></wp:post_parent>
<wp:menu_order></wp:menu_order>
<wp:post_type>post</wp:post_type>
<wp:post_password></wp:post_password>

<wp:postmeta>
	<wp:meta_key>country</wp:meta_key>
	<wp:meta_value>sweden</wp:meta_value>
</wp:postmeta>
</item>

I wonder if it is ok to leave out the below or just keep them empty?

wp:post_id
wp:post_date
wp:post_date_gmt
wp:comment_status
wp:ping_status
wp:post_name
wp:post_parent
wp:menu_order
wp:post_password