Understand the "xml" namespace prefix when parsing into the DOM

This does not yet *do* anything with the attributes; it only stops
them from preventing a successful parse.

Related to #46

src/lib.rs

@@ -72,6 +72,9 @@ pub mod writer;
 
 pub use str::XmlChar;
 
+static XML_NS_PREFIX: &'static str = "xml";
+static XML_NS_URI:    &'static str = "http://www.w3.org/XML/1998/namespace";
+
 /// A prefixed name. This represents what is found in the string form
 /// of an XML document, and does not apply any namespace mapping.
 #[derive(Debug,Copy,Clone,PartialEq,Eq,PartialOrd,Ord)]

src/parser.rs

@@ -798,6 +798,7 @@ struct DomBuilder<'d> {
     elements: Vec<dom::Element<'d>>,
     element_names: Vec<Span<PrefixedName<'d>>>,
     attributes: Vec<DeferredAttribute<'d>>,
+    seen_top_element: bool,
 }
 
 impl<'d> DomBuilder<'d> {
@@ -807,6 +808,7 @@ impl<'d> DomBuilder<'d> {
             elements: vec![],
             element_names: Vec::new(),
             attributes: Vec::new(),
+            seen_top_element: false,
         }
     }
 
@@ -879,6 +881,11 @@ impl<'d> DomBuilder<'d> {
             element.register_prefix(*prefix, ns_uri);
         }
 
+        if !self.seen_top_element {
+            self.seen_top_element = true;
+            element.register_prefix(::XML_NS_PREFIX, ::XML_NS_URI);
+        }
+
         self.append_to_either(element);
         self.elements.push(element);
 
@@ -1326,6 +1333,21 @@ mod test {
         assert_eq!(attr.value(), "b");
     }
 
+    #[test]
+    fn an_attribute_with_xml_space_preserve() {
+        let package = quick_parse("<hello xml:space='preserve'> <a/> </hello>");
+        let doc = package.as_document();
+        let top = top(&doc);
+
+        assert_eq!(top.attribute((::XML_NS_URI, "space")).unwrap().value(), "preserve");
+
+        let children = top.children();
+        assert_eq!(children.len(), 3);
+        assert_eq!(children[0].text().unwrap().text(), " ");
+        assert_qname_eq!(children[1].element().unwrap().name(), "a");
+        assert_eq!(children[2].text().unwrap().text(), " ");
+    }
+
     #[test]
     fn an_attribute_with_references() {
         let package = quick_parse("<log msg='I &lt;3 math' />");

src/raw.rs

@@ -6,9 +6,6 @@ use string_pool::{StringPool,InternedString};
 use std::marker::PhantomData;
 use std::slice;
 
-static XML_NS_PREFIX: &'static str = "xml";
-static XML_NS_URI:    &'static str = "http://www.w3.org/XML/1998/namespace";
-
 struct InternedQName {
     namespace_uri: Option<InternedString>,
     local_part: InternedString,
@@ -644,7 +641,7 @@ impl Connections {
     {
         let mut namespaces = Vec::new();
 
-        namespaces.push((XML_NS_PREFIX, XML_NS_URI));
+        namespaces.push((::XML_NS_PREFIX, ::XML_NS_URI));
 
         let all_namespaces =
             self.element_parents(element)