Stylesheet Query String

How does Rails come up with the query string appended to the
stylesheet tag?

The API does not even show a query string being appended:
http://api.rubyonrails.com/classes/ActionView/Helpers/AssetTagHelper.html#M001499

I thought it was a function of the file timestamp, but I have updated
the file and the querystring still hasn’t changed. I just don’t want
my users to have to refresh to force their browser to see the new
stylesheet.

Thanks!
Tom

I never saw a reply to this post? Is my question hard or dumb? :slight_smile: