This function expands XInclude directives in-place in tree pointed by elem. elem is either the root Element or an ElementTree instance to find such element. loader is an optional resource loader. If omitted, it defaults to default_loader(). If given, it should be a callable that implements the same interface as default_loader(). base_url is base URL of the original file, to resolve relative include file references. max_depth is the maximum number of recursive inclusions. Limited to reduce the risk of malicious content explosion. Pass None to disable the limitation.