diff --git a/gui/header/window-buttons.xml b/gui/header/window-buttons.xml
index f594b9efe..ef22f25ee 100644
--- a/gui/header/window-buttons.xml
+++ b/gui/header/window-buttons.xml
@@ -6,7 +6,7 @@
 		<if :a="{{IS_MAXIMIZED}}">
 			<icon :svg="`window_restore_down.svg`" />
 		</if>
-		<if :a="{{IS_MAXIMIZED}}" b="false">
+		<if :a="{{IS_MAXIMIZED}}" :b="false">
 			<icon :svg="`maximize.svg`" />
 		</if>
 	</box>
diff --git a/src/layout_abstract_syntax.rs b/src/layout_abstract_syntax.rs
index 60903e03e..cc92b3ec2 100644
--- a/src/layout_abstract_syntax.rs
+++ b/src/layout_abstract_syntax.rs
@@ -20,7 +20,11 @@ impl LayoutAbstractNode {
 pub struct LayoutAbstractTag {
 	pub namespace: String,
 	pub name: String,
+	/// Layout attributes, which are used by the layout engine.
 	pub layout_attributes: LayoutAttributes,
+	/// The special content attribute, representing the inner elements of this tag.
+	pub content: Option<AttributeValue>,
+	/// User-defined attributes, which are prefixed with ':'
 	pub attributes: Vec<Attribute>,
 }
 
@@ -30,12 +34,25 @@ impl LayoutAbstractTag {
 			namespace,
 			name,
 			layout_attributes: Default::default(),
+			content: None,
 			attributes: Vec::new(),
 		}
 	}
 
 	pub fn add_attribute(&mut self, attribute: Attribute) {
+		// User-defined attribute
+		if attribute.name.chars().next().unwrap() == ':' {
+			self.attributes.push(attribute);
+		}
+		else {
+			self.add_builtin_attribute(attribute);
+		}
+	}
+
+	fn add_builtin_attribute(&mut self, attribute: Attribute) {
 		match &attribute.name[..] {
+			// The special `content` attribute
+			"content" => self.content = Some(attribute.value),
 			// Layout attributes, stored separately
 			"width" => self.layout_attributes.width = attribute.dimension(),
 			"height" => self.layout_attributes.height = attribute.dimension(),
@@ -47,8 +64,7 @@ impl LayoutAbstractTag {
 			"x-spacing" => self.layout_attributes.spacing.set_horizontal(attribute.dimension()),
 			"y-spacing" => self.layout_attributes.spacing.set_vertical(attribute.dimension()),
 			"spacing" => self.layout_attributes.spacing = attribute.box_dimensions(),
-			// Non-layout attribute
-			_ => self.attributes.push(attribute),
+			_ => panic!("unknown builtin attribute {}", attribute.name),
 		}
 	}
 }
diff --git a/src/layout_system.rs b/src/layout_system.rs
index 23b3278a1..d14874e59 100644
--- a/src/layout_system.rs
+++ b/src/layout_system.rs
@@ -317,29 +317,26 @@ impl LayoutSystem {
 		for node in component {
 			println!("Printing Component:\n{:#?}\n\n", node);
 			match node {
-				LayoutAbstractNode::Tag(tag) => {
-					let content = tag.attributes.iter().find(|a| a.name == "content");
-					match content {
-						Some(attribute) => match attribute.value {
-							AttributeValue::TypeValue(ref type_value) => {
-								for type_value_or_argument in type_value {
-									match type_value_or_argument {
-										TypeValueOrArgument::TypeValue(type_value) => match type_value {
-											TypeValue::Layout(layout) => {
-												for component_ast in layout {
-													Self::print_layout_tree(&component_ast);
-												}
-											},
-											_ => {},
+				LayoutAbstractNode::Tag(ref tag) => match tag.content {
+					Some(ref value) => match value {
+						AttributeValue::TypeValue(ref type_value) => {
+							for type_value_or_argument in type_value {
+								match type_value_or_argument {
+									TypeValueOrArgument::TypeValue(type_value) => match type_value {
+										TypeValue::Layout(layout) => {
+											for component_ast in layout {
+												Self::print_layout_tree(&component_ast);
+											}
 										},
-										TypeValueOrArgument::VariableArgument(_) => {},
-									}
+										_ => {},
+									},
+									TypeValueOrArgument::VariableArgument(_) => {},
 								}
-							},
-							AttributeValue::VariableParameter(_) => {},
+							}
 						},
-						None => {},
-					}
+						AttributeValue::VariableParameter(_) => {},
+					},
+					None => {},
 				},
 				LayoutAbstractNode::Text(_) => {},
 			}