原文：
Whilst the 4.4 release predominantly focussed on performance and optimisation, there were a number of other enhancements added to the release (as always the changelog is the best place to view changes). One of these, that should be of interest to skinners and those interested in accessibility standards & xhtml compliance, is support for skin level doctypes .
Historically, if you wanted to target your skin/container for a particular version of html/xhtml, you had to manually edit the default.aspx page to alter the hardcoded DOCTYPE declaration. With 4.4, the declaration has been made dynamic, to allow users to declare particular doctypes with particular skins. To make use of this, you create a file with the same name as your skin except ending in doctype.xml (rather than ascx/htm/html) and it’ll be picked up during skin load. This xml file should contain a single node,SkinDocType, that contains a declaration of your desired doctype. To ensure that the parser reads the value correctly, you need to use a CDATA section to escape out the various < and & characters e.g. If I have a skin called mypage.asx that I intended to render as XHTML 1.0 strict, then I would create a file called mypage.doctype.xml which would contain the following:
<SkinDocType><![CDATA[<!DOCTYPE XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">]]></SkinDocType>
对此John Mitchell认为这个解决方案不灵活，每次页面加载的XML解析会降低效率，他提出的解决方案如下：
原文：
Brand new in DNN 4.4 is the option to change your Doctype which Cathal blogged about.
As Cathal pointed out in this thread the implementation will need to be improved for performance because on every request the DNN framework is looking for an XML file and loading it into an XML Document to validate the XML.
There is also concern that it is hard to implement with multiple skins because you would need a different XML file for every Skin.
You can shortcut all of this now and not take the performance hit by using the code below.
Just copy and paste the following code directly into your HTML or .ASCX skin file.
时间有限，就不翻译了，贴出来供大家参考。