Index: src/OFXMLElement.h
==================================================================
--- src/OFXMLElement.h
+++ src/OFXMLElement.h
@@ -207,35 +207,74 @@
  */
 - (OFString*)stringValue;
 
 /**
  * Adds the specified attribute.
+ *
+ * If an attribute with the same name and namespace already exists, it is not
+ * added.
  *
  * \param attr The attribute to add
  */
 - (void)addAttribute: (OFXMLAttribute*)attr;
 
 /**
  * Adds the specified attribute with the specified value.
+ *
+ * If an attribute with the same name and namespace already exists, it is not
+ * added.
  *
  * \param name The name of the attribute
  * \param value The value of the attribute
  */
 - (void)addAttributeWithName: (OFString*)name
 		 stringValue: (OFString*)value;
 
 /**
  * Adds the specified attribute with the specified namespace and value.
+ *
+ * If an attribute with the same name and namespace already exists, it is not
+ * added.
  *
  * \param name The name of the attribute
  * \param ns The namespace of the attribute
  * \param value The value of the attribute
  */
 - (void)addAttributeWithName: (OFString*)name
 		   namespace: (OFString*)ns
 		 stringValue: (OFString*)value;
 
+/**
+ * \param attrname The name of the attribute
+ * \return The attribute with the specified name
+ */
+- (OFXMLAttribute*)attributeForName: (OFString*)attrname;
+
+/**
+ * \param attrname The name of the attribute
+ * \param attrns The namespace of the attribute
+ * \return The attribute with the specified name and namespace
+ */
+- (OFXMLAttribute*)attributeForName: (OFString*)attrname
+			  namespace: (OFString*)attrns;
+
+/**
+ * Removes the attribute with the specified name.
+ *
+ * \param attrname The name of the attribute
+ */
+- (void)removeAttributeForName: (OFString*)attrname;
+
+/**
+ * Removes the attribute with the specified name and namespace.
+ *
+ * \param attrname The name of the attribute
+ * \param attrns The namespace of the attribute
+ */
+- (void)removeAttributeForName: (OFString*)attrname
+		     namespace: (OFString*)attrns;
+
 /**
  * Sets a prefix for a namespace.
  *
  * \param prefix The prefix for the namespace
  * \param ns The namespace for which the prefix is set

Index: src/OFXMLElement.m
==================================================================
--- src/OFXMLElement.m
+++ src/OFXMLElement.m
@@ -422,29 +422,21 @@
 						       selector: _cmd];
 
 	if (attributes == nil)
 		attributes = [[OFMutableArray alloc] init];
 
-	/* FIXME: Prevent having it twice! */
-
-	[attributes addObject: attr];
+	if ([self attributeForName: attr->name
+			 namespace: attr->ns] == nil)
+		[attributes addObject: attr];
 }
 
 - (void)addAttributeWithName: (OFString*)name_
 		 stringValue: (OFString*)value
 {
-	OFAutoreleasePool *pool;
-
-	if (name == nil)
-		@throw [OFInvalidArgumentException newWithClass: isa
-						       selector: _cmd];
-
-	pool = [[OFAutoreleasePool alloc] init];
-	[self addAttribute: [OFXMLAttribute attributeWithName: name_
-						    namespace: nil
-						  stringValue: value]];
-	[pool release];
+	[self addAttributeWithName: name_
+			 namespace: nil
+		       stringValue: value];
 }
 
 - (void)addAttributeWithName: (OFString*)name_
 		   namespace: (OFString*)ns_
 		 stringValue: (OFString*)value
@@ -460,12 +452,69 @@
 						    namespace: ns_
 						  stringValue: value]];
 	[pool release];
 }
 
-/* TODO: Replace attribute */
-/* TODO: Remove attribute */
+- (OFXMLAttribute*)attributeForName: (OFString*)attrname
+{
+	return [self attributeForName: attrname
+			    namespace: nil];
+}
+
+- (OFXMLAttribute*)attributeForName: (OFString*)attrname
+			  namespace: (OFString*)attrns
+{
+	OFXMLAttribute **attrs_c = [attributes cArray];
+	size_t i, attrs_count = [attributes count];
+
+	if (attrns != nil) {
+		for (i = 0; i < attrs_count; i++)
+			if ([attrs_c[i]->ns isEqual: attrns] &&
+			    [attrs_c[i]->name isEqual: attrname])
+				return attrs_c[i];
+	} else {
+		for (i = 0; i < attrs_count; i++)
+			if (attrs_c[i]->ns == nil &&
+			    [attrs_c[i]->name isEqual: attrname])
+				return attrs_c[i];
+	}
+
+	return nil;
+}
+
+- (void)removeAttributeForName: (OFString*)attrname
+{
+	[self removeAttributeForName: attrname
+			   namespace: nil];
+}
+
+- (void)removeAttributeForName: (OFString*)attrname
+		     namespace: (OFString*)attrns
+{
+	OFXMLAttribute **attrs_c = [attributes cArray];
+	size_t i, attrs_count = [attributes count];
+
+	if (attrns != nil) {
+		for (i = 0; i < attrs_count; i++) {
+			if ([attrs_c[i]->ns isEqual: attrns] &&
+			    [attrs_c[i]->name isEqual: attrname]) {
+				[attributes removeObjectAtIndex: i];
+
+				return;
+			}
+		}
+	} else {
+		for (i = 0; i < attrs_count; i++) {
+			if (attrs_c[i]->ns == nil &&
+			    [attrs_c[i]->name isEqual: attrname]) {
+				[attributes removeObjectAtIndex: i];
+
+				return;
+			}
+		}
+	}
+}
 
 - (void)setPrefix: (OFString*)prefix
      forNamespace: (OFString*)ns_
 {
 	if (name == nil || prefix == nil || [prefix isEqual: @""])

Index: tests/OFXMLElementTests.m
==================================================================
--- tests/OFXMLElementTests.m
+++ tests/OFXMLElementTests.m
@@ -92,13 +92,24 @@
 
 	TEST(@"-[addAttributeWithName:namespace:stringValue:]",
 	    R([elem[1] addAttributeWithName: @"foo"
 				  namespace: @"urn:objfw:test"
 				stringValue: @"bar"]) &&
+	    R([elem[1] addAttributeWithName: @"foo"
+				  namespace: @"urn:objfw:test"
+				stringValue: @"ignored"]) &&
 	    [[elem[1] stringValue] isEqual:
 	    @"<foo foo='b&amp;ar' objfw-test:foo='bar'>b&amp;ar</foo>"])
 
+	TEST(@"-[removeAttributeForName:namespace:]",
+	    R([elem[1] removeAttributeForName: @"foo"]) &&
+	    [[elem[1] stringValue] isEqual:
+	    @"<foo objfw-test:foo='bar'>b&amp;ar</foo>"] &&
+	    R([elem[1] removeAttributeForName: @"foo"
+				    namespace: @"urn:objfw:test"]) &&
+	    [[elem[1] stringValue] isEqual: @"<foo>b&amp;ar</foo>"])
+
 	TEST(@"-[addChild:]",
 	    R([elem[0] addChild: [OFXMLElement elementWithName: @"bar"]]) &&
 	    [[elem[0] stringValue] isEqual:
 	    @"<foo foo='b&amp;ar'><bar/></foo>"] &&
 	    R([elem[2] addChild: [OFXMLElement elementWithName: @"bar"