Conditional comments are conditional statements interpreted by Microsoft Internet Explorer versions 5 through 9 in HTML source code. They can be used to provide and hide code to and from these versions of Internet Explorer. Conditional comments are not supported in Internet Explorer 10 and 11.
Conditional comments in HTML[1] first appeared in Microsoft's Internet Explorer 5 browser, although support has now been deprecated. In Internet Explorer 10, HTML conditional comments are not supported when the page is in standards mode (document mode 10).[2] JScript conditional comments were introduced in Internet Explorer 4, and they continued to be supported in Internet Explorer 10, in standards mode or compatibility mode.