fix

packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js

@@ -2041,9 +2041,8 @@ export const template_visitors = {
 			if (attribute.type === 'Attribute') {
 				if (attribute.name === 'xmlns' && !is_text_attribute(attribute)) {
 					dynamic_namespace = attribute.value;
-				} else {
-					attributes.push(attribute);
 				}
+				attributes.push(attribute);
 			} else if (attribute.type === 'SpreadAttribute') {
 				attributes.push(attribute);
 			} else if (attribute.type === 'ClassDirective') {

packages/svelte/src/internal/client/dom/blocks/svelte-element.js

@@ -69,7 +69,11 @@ export function element(anchor, get_tag, is_svg, render_fn, get_namespace) {
 
 		block(() => {
 			const next_tag = get_tag() || null;
-			const ns = get_namespace?.() || (is_svg || next_tag === 'svg' ? namespace_svg : null);
+			const ns = get_namespace
+				? get_namespace()
+				: is_svg || next_tag === 'svg'
+					? namespace_svg
+					: null;
 			// Assumption: Noone changes the namespace but not the tag (what would that even mean?)
 			if (next_tag === tag) return;
 

packages/svelte/tests/runtime-runes/samples/dynamic-element-dynamic-namespace/main.svelte

@@ -5,7 +5,7 @@
 
 <button onclick={() => {
 	tag = 'div';
-	xmlns = 'http://www.w3.org/1999/xhtml';
+	xmlns = null;
 }}>change</button>
 
 <!-- wrapper necessary or else jsdom says this is always an xhtml namespace -->

packages/svelte/types/index.d.ts

@@ -1539,10 +1539,10 @@ declare module 'svelte/compiler' {
 		tag: Expression;
 		metadata: {
 			/**
-			 * `true`/`false` if this is definitely (not) an svg element.
-			 * `null` means we can't know statically.
+			 * `true` if this is an svg element. The boolean may not be accurate because
+			 * the tag is dynamic, but we do our best to infer it from the template.
 			 */
-			svg: boolean | null;
+			svg: boolean;
 			scoped: boolean;
 		};
 	}