XAML Syntax Basics

Because XAML is XML, it inherits XML's well-formedness rules: a single root element, properly nested and closed tags, and case-sensitive names. On top of that XML foundation, XAML defines specific conventions — object elements that instantiate classes, attributes that set simple properties, and nested elements that set complex properties or add children. Understanding these base rules is what lets you read any WPF, UWP, or .NET MAUI XAML file, even one you've never seen before, and know exactly what object graph it produces.

The most common syntax is the object element with attributes, such as <Button Content="OK" Width="80"/>, where the tag name creates a Button and each attribute sets a simple property from a string. When a property's value is too complex to express as a string — for example, setting a Button's Content to an Image rather than plain text — XAML uses property element syntax, written as <Button.Content><Image Source="icon.png"/></Button.Content>, where the dot-separated tag name identifies exactly which property on the parent is being set.

Many container classes designate one property as their ContentProperty via a .NET attribute, which lets XAML omit the property-element wrapper entirely: a StackPanel's default content property is Children, so <StackPanel><Button/><Button/></StackPanel> directly nests two buttons without ever writing <StackPanel.Children>. Collections work similarly — <Grid.RowDefinitions><RowDefinition Height="Auto"/><RowDefinition Height="*"/></Grid.RowDefinitions> implicitly adds each RowDefinition to the underlying RowDefinitionCollection because collection properties accept multiple child elements automatically.

Curly-brace syntax like {Binding Path=UserName} or {StaticResource PrimaryBrush} invokes a markup extension — a class implementing MarkupExtension whose ProvideValue method computes the actual value to assign, rather than XAML converting a literal string. This is how XAML expresses things that aren't literal values at all, such as a data binding to a property on a ViewModel, a reference to a resource declared elsewhere, or a static value like {x:Static SystemColors.WindowBrush}, all inside what still looks like an ordinary attribute.