wordpress css background image parameter

i was studying on wordpress administration theme.

i notice somethig i've never seen before:

.meta-box-sortables .postbox:hover .handlediv{background:transparent url(..开发者_运维知识库/images/menu-bits.gif?ver=20100610) no-repeat scroll left -111px;}

what does '?ver=20100610' mean?

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On a .gif image, most likely nothing. It's probably there for no reason other than as a quick-and-dirty means of bypassing caching when the developer/designer update the theme to a new version (presumably the value of 'ver' would change to the new release date, forcing browsers and proxies to retrieve the potentially-changed image file anew from the server instead of using their cached version).