Serialize empty attribute values without =""

src/rewritable_units/element.rs

@@ -1593,6 +1593,26 @@ mod tests {
             );
         }
 
+        #[test]
+        fn add_valueless_attr() {
+            test!(
+                |el| {
+                    el.set_attribute("a5", "").unwrap();
+                },
+                r#"<a a1='foo " baré " baz' a2="foo ' bar ' baz" a3=foo/bar a4 a5></a>"#
+            );
+        }
+
+        #[test]
+        fn clear_value_to_valueless_attr() {
+            test!(
+                |el| {
+                    el.set_attribute("a2", "").unwrap();
+                },
+                r#"<a a1='foo " baré " baz' a2 a3=foo/bar a4></a>"#
+            );
+        }
+
         #[test]
         fn self_closing_flag() {
             // NOTE: we should add space between valueless attr and self-closing slash

src/rewritable_units/tokens/attributes.rs

@@ -144,6 +144,8 @@ impl Serialize for &Attribute<'_> {
     fn into_bytes(self, output_handler: &mut dyn FnMut(&[u8])) -> Result<(), RewritingError> {
         if let Some(raw) = self.raw.as_ref() {
             output_handler(raw);
+        } else if self.value.is_empty() {
+            output_handler(&self.name);
         } else {
             output_handler(&self.name);
             output_handler(b"=\"");