Normally, result tree serialization escapes& and < (and possibly other characters) when outputting text nodes. This ensures that the output is well-formed XML. However, it is sometimes convenient to be able to produce output that is almost, but not quite well-formed XML; for example, the output may include ill-formed sections that will be transformed into well-formed XML by a subsequent non-XML aware process. If a processing instruction is sent with this name, serialization should be output without any escaping.

Result DOM trees may also have PI_DISABLE_OUTPUT_ESCAPING and PI_ENABLE_OUTPUT_ESCAPING inserted into the tree.

If the Result is not to be written to a file, the system identifier is optional. The application may still want to provide one, however, for use in error messages and warnings, or to resolve relative output identifiers.