fix: Use correct case for XML (SVG) elements

Previously XML elements which use some upper case letters would be
converted to all-lowercase during string parsing. As xml is
case-sensitive, this breaks the element. An example is the XML
linearGradient.

This was caused by the code incorrectly converting all element names to
lowercase to ensure HTML tags are correctly assigned, as they use lower
case internally, but the browser function tagName returns all caps for
HTML tags.

Fix this by only converting HTML element names to lower case.

Fix: #377

src/browser/dom/virtual_dom_bridge.rs

@@ -315,11 +315,11 @@ impl<Ms> From<&web_sys::Element> for El<Ms> {
     /// and markdown strings. Includes children, recursively added.
     #[allow(clippy::too_many_lines)]
     fn from(ws_el: &web_sys::Element) -> Self {
-        // Result of tag_name is all caps, but tag From<String> expects lower.
-        // Probably is more pure to match by xlmns attribute instead.
-        let mut el = match ws_el.tag_name().to_lowercase().as_ref() {
-            "svg" => El::empty_svg(ws_el.tag_name().to_lowercase().into()),
-            _ => El::empty(ws_el.tag_name().to_lowercase().into()),
+        let namespace = ws_el.namespace_uri().map(Namespace::from);
+        let mut el = match namespace {
+            // tag_name returns all caps for HTML, but Tag::from uses lowercase names for HTML
+            Some(Namespace::Html) => El::empty(ws_el.tag_name().to_lowercase().into()),
+            _ => El::empty(ws_el.tag_name().into()),
         };
 
         // Populate attributes
@@ -420,14 +420,14 @@ impl<Ms> From<&web_sys::Element> for El<Ms> {
             "solidcolor",
         ];
 
-        if svg_tags.contains(&ws_el.tag_name().to_lowercase().as_str()) {
+        if svg_tags.contains(&ws_el.tag_name().as_str()) {
             el.namespace = Some(Namespace::Svg);
         }
 
-        if let Some(ns) = ws_el.namespace_uri() {
+        if let Some(ref ns) = namespace {
             // Prevent attaching a `xlmns` attribute to normal HTML elements.
-            if ns != "http://www.w3.org/1999/xhtml" {
-                el.namespace = Some(ns.into());
+            if ns != &Namespace::Html {
+                el.namespace = namespace;
             }
         }