node: add attr_mut helper method

src/node/mod.rs

@@ -150,6 +150,11 @@ impl Node {
     self.attributes.as_ref()
   }
 
+  #[inline]
+  pub fn attributes_mut(&mut self) -> Option<&mut IndexMap<String, String>> {
+    self.attributes.as_mut()
+  }
+
   #[inline]
   pub fn children(&self) -> Option<&Vec<Node>> {
     self.children.as_ref()
@@ -181,6 +186,12 @@ impl Node {
     })
   }
 
+  pub fn attr_mut(&mut self, key: &str) -> Option<&mut String> {
+    self.attributes_mut().and_then(|attributes| {
+      attributes.get_mut(key)
+    })
+  }
+
   pub fn into_key_and_value(self) -> (String, Option<Value>) {
     (self.key, self.value)
   }