Like it or not, but XML has become quite common and is showing up in questions that are not directly related to XML at all (i.e. the question is not about parsing/reading/handling the XML, but the XML shows up as context, for example).
A good example is this question (and many other android-related questions).
Since the question has the java tag it (rightfully) assumes that source in it is Java code.
This means that Java syntax highlighting is also applied to the XML which has strange results (for example the blue package
statement).
It might be a good idea to check the first 5 letters of a code-block and if they are <?xml
then override all other auto-detection and format it as XML.
I'm aware that this would give XML a special state (since no other language gets that kind of special treatment, as far as I know), but it's pervasiveness does ask for this.