From this article Interoperable HTML5 Quirks Mode in IE10, the HTML5-based quirks mode is the default quirks mode in IE10 for those pages without a DOCTYPE or X-UA-Compatible tag. IE's legacy quirks mode is now referred to as Internet Explorer 5 quirks.
In the official IE10, it is. But not in the WebBrowser control. The default quirks mode is IE5 quirks in the WebBrowser control application.
For example: for a simplest html page that without DOCTYPE or X-UA-Compatible tag:
<html><head><metacharset="UTF-8"/><title>Get documentMode!</title></head><body><h2>document.documentMode</h2><p><script>
document.write(document.documentMode);</script><p></body></html>The documentMode = 10 in Official IE10, but the documentMode = 5 in WebBrowser control application ( before test, I have added the registry item value: HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_BROWSER_EMULATION\MyApp.exe to 10000, or 10001 in decimal).
Why the behavior is different? How can I configure the default quirks mode of WebBrowser control application to "HTML5-based quirks mode" ?