'application' indicates whether or not the element points to an HTA application
<HTML>
<Title>Example For application</Title>
<BODY>
<iframe application="yes"
src="http://www.java2s.com/style/logo.png"
style="width:40%;">
</iframe>
<iframe application="no"
src="http://www.java2s.com/style/logo.png"
style="width: 40%;">
</iframe>
</BODY>
</HTML>
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