The standard Scala XML library. Please file issues here instead of over at issues.scala-lang.org.
Since Scala 2.11, this library is a separate jar that can be omitted from Scala projects that do not use XML. If you are cross-building a project that uses scala-xml with both Scala 2.10 and later Scala versions, take a look this example.
The compiler was decoupled from this particular implementation using the same approach as for comprehensions (XML syntax is desugared into a set of method calls, which unfortunately is only defined by the implementation). Alternative implementations are welcome!
API documentation is available here.
Security best practices
The XML spec has some features that are best turned off, to avoid unsavory things like file system access, DoS attacks,... Issue #17 tracks the recommended way of configuring the XML parser used by scala-xml to avoid these. This is by no means an exhaustive list. We'll be happy to incorporate your suggestions -- just comment on the ticket!