docs: note comments within tags possibility (#18482)

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>

documentation/docs/03-template-syntax/01-basic-markup.md

@@ -215,3 +215,14 @@ You can add a special comment starting with `@component` that will show up when
 	</h1>
 </main>
 ````
+
+You can also put JavaScript-style comments within tags between attributes:
+
+```svelte
+<div
+  // this is a comment!
+  data-foo="bar"
+>
+  foo bar
+</div>
+```