Most current browsers can read and display an XML file as a data structure. Any facility past this is created by either utilization of a pre-existing definition accepted or promulgated by the Browser developer, or the presence of a plug-in that provides the tools that provide the means of interpreting this data.
Still doesn’t mean it is “server side”. Nice attempt at buzzword bingo, but XML is and can be read on clients of all types in all kinds of applications. It is every bit as client side as a programmer wants it to be.