Parse classes during XAML compilation.

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/AvaloniaXamlIlLanguageParseIntrinsics.cs

@@ -198,6 +198,15 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions
                 return ConvertDefinitionList(node, text, types, types.RowDefinitions, types.RowDefinition, "row definitions", out result);
             }
 
+            if (type.Equals(types.Classes))
+            {
+                var classes = text.Split(' ');
+                var classNodes = classes.Select(c => new XamlConstantNode(node, types.XamlIlTypes.String, c)).ToArray();
+
+                result = new AvaloniaXamlIlAvaloniaListConstantAstNode(node, types, types.Classes, types.XamlIlTypes.String, classNodes);
+                return true;
+            }
+
             result = null;
             return false;
         }

src/Markup/Avalonia.Markup.Xaml.Loader/CompilerExtensions/Transformers/AvaloniaXamlIlWellKnownTypes.cs

@@ -77,6 +77,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
         public IXamlType RowDefinitions { get; }
         public IXamlType ColumnDefinition { get; }
         public IXamlType ColumnDefinitions { get; }
+        public IXamlType Classes { get; }
 
         public AvaloniaXamlIlWellKnownTypes(TransformerConfiguration cfg)
         {
@@ -166,6 +167,7 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
             ColumnDefinitions = cfg.TypeSystem.GetType("Avalonia.Controls.ColumnDefinitions");
             RowDefinition = cfg.TypeSystem.GetType("Avalonia.Controls.RowDefinition");
             RowDefinitions = cfg.TypeSystem.GetType("Avalonia.Controls.RowDefinitions");
+            Classes = cfg.TypeSystem.GetType("Avalonia.Controls.Classes");
         }
     }