Some consumers of XML files require an explicit DOCTYPE to accept an XML file. data.xml does not currently support the specification of doctypes when emitting XML. When XML is parsed, I believe DOCTYPEs are silently ignored, so there is no representation in the data model for them. The best design is possibly an :doctype option in clojure.data.xml/emit ?

I've attached a web.xml as example.

XML parsers can support preserving white space nodes, but clojure.data.xml does not seem to support this functionality.

For example, the following should be able to return true (perhaps with an option to parse-str):

(= (clojure.data.xml/element :x {}
                             (clojure.data.xml/element :a {} "foo")
                             " "
                             (clojure.data.xml/element :a {} "bar"))
   (clojure.data.xml/parse-str
     (str "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
          "<x>"
          "<a>foo</a>"
          " "
          "<a>bar</a>"
          "</x>")))
;=> true

This is the current behavior:

(= (clojure.data.xml/element :x {}
                             (clojure.data.xml/element :a {} "foo")
                             (clojure.data.xml/element :a {} "bar"))
   (clojure.data.xml/parse-str
     (str "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
          "<x>"
          "<a>foo</a>"
          " "
          "<a>bar</a>"
          "</x>")))
;=> true

I can create an element with a boolean value but I can't emit it...

user=> (emit-str (element :something {} false))
IllegalArgumentException No implementation of method: :gen-event of protocol: #'clojure.data.xml/EventGeneration found for class: java.lang.Boolean clojure.core/-cache-protocol-fn (core_deftype.clj:541)

Observe:

> (x/emit-str (x/element :NC {"xmlns" "http://example.com" "xmlns:xsi" "http://www.w3.org/2001/XMLSchema-instance" "xsi:schemaLocation" "http://www.example.com/schema.xsd"} (x/element :Foo {} "bar")))
"<?xml version=\"1.0\" encoding=\"UTF-8\"?><NC xsi:schemaLocation=\"http://www.example.com/schema.xsd\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns=\"http://example.com\"><Foo>bar</Foo></NC>"
> (x/parse-str *1)
#clojure.data.xml.Element{:tag :NC, :attrs {:xsi/schemaLocation "http://www.example.com/schema.xsd"}, :content (#clojure.data.xml.Element{:tag :Foo, :attrs {}, :content ("bar")})}
a> (x/emit-str *1)
XMLStreamException Prefix cannot be null com.sun.xml.internal.stream.writers.XMLStreamWriterImpl.writeAttribute (XMLStreamWriterImpl.java:574)
app.services.external.experian.internal.test-data>

(a) the xmlns and xmlns:xsi attributes have disappeared. Not the point of this issue but worth pointing out.
(b) "xsi:schemaLocation" has become :xsi/schemaLocation
(c) emitting a string blows up.

Add support for both parsing and emitting namespace qualified tags and namespaces URI declarations.
It basically follows the underlying Java XML API in giving xmlns:foo attributes "special" treatment.

Solvable with a type hint on emit-cdata arg 'writer'