If-Modified-Since HTTP header passed by IE9 includes length?

[Twizted]

In my ASP.NET 4.0 web app, I've got a generic handler (.ashx) that serves images stored in the DB. In the interest of efficiency, I'm handling some caching-related headers and passing cache information.I'm getting DateTime parse errors moderately frequently from trying to parse the \[code\]If-Modified-Since\[/code\] header contents, usually from IE9. Turns out it's sending something like this:\[quote\] Mon, 28 Nov 2011 16:34:52 GMT; length=8799\[/quote\]I'm handling that by using a regular expression to strip out the last part. But I'm curious: what length is it referring to, and what use is it? Is it the size of the cached data for the requested URL?