Alternative markup syntax proposal.

Since the very first thing XamlIl does is conversion of XML to its own AST, we can now create other markup languages relatively cheaply by simply writing a parser that produces the same AST.

Since some people seem to hate XML, here is a non-XML markup proposal:

// Default namespaces for Avalonia, x: and d: are omitted here and added automatically
using local = clr MyNamespace
using lib = xml http://some.lib/xml/namespace
Window 
{
     StackPanel
     {
          // Equivalent of <Button>
          Button
          // Unless followed by = before the end of line, in this case it's a property assignment
          Orientation = "Horizontal"
          Attached.Property="Value"
          // This is an equivalent of <Button Background="Red">Click me</Button>
          Button
          {
               "Click me"
               Background = "Red"
          }
          local:MyControl
          lib:LibraryControl
          clr:System.Collections.Generic.List<clr:System.Int32> {
                1
                2
                3 4 5 6
          }
          // Markup extensions are prefixed by $
          TextBlock { Text = ${Binding SomeVmProp} }
          // $-prefixed strings are a shortcut to {Binding ...}
          TextBlock { x:Name = "Name" Text = $"SomeVmProp" }
          TextBlock { Text = $"#Name.Text, Mode=TwoWay" }
          TextBlock {
                  "Plain text"
                  Run { Background="Red" "Text" FontFamily="Tahoma" }
                  "Plain text"
          }
     }
     Styles = 
     {
          // Styles property is treated in specific way, all root elements are considered to be <Style Selector="{LINE}"> to reduce boilerplate
          StackPanel > is:(Control).someClass:pointerover
          {
                Margin = "0 0 1 4"
          }
          Button
          {
                Template =
                {
                     // ControlTemplate is omitted here and is assumed by default. We can probably do the same for regular XAML
                     ContentPresenter
                     {
                           Name = "PART_ContentPresenter"
                           Background = ${TemplateBinding Background}
                           TextBlock.Foreground = ${TemplateBinding Foreground}
                     }
                }
          }
     }
}

XAML for comparison:

<Window 
   xmlns="https://github.com/avaloniaui"
   xmlns:local="clr-namespace:MyNamespace"
   xmlns:lib="http://some.lib/xml/namespace"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   xmlns:scg="clr-namespace:System.Collections.Generic;assembly=netstandard">
   xmlns:sys="clr-namespace:System;assembly=netstandard">
  <StackPanel 
     Orientation="Horizontal" Attached.Property="Value">
     <Button>
     <Button Background="Red">
        Click me
     </Button>
     <local:MyControl/>
     <lib:LibraryControl/>
     <scg:List x:TypeArguments="sys:Int32">
       <x:Int32>1</x:Int32>
       <x:Int32>2</x:Int32>
       <x:Int32>3</x:Int32>
       <x:Int32>4</x:Int32>
       <x:Int32>5</x:Int32>
       <x:Int32>6</x:Int32>
     </scg:List>
     <TextBlock Text="{Binding SomeVmProp}"/>
     <TextBlock x:Name="Name" Text="{Binding SomeVmProp}"/>
     <TextBlock Text="{Binding #Name.Text, Mode=TwoWay}"/>
     <TextBlock>
        Plain text
        <Run Background="Red" FontFamily="Tahoma">Text</Run>
        Plain text
     </TextBlock>
   </StackPanel>
   <Window.Styles>
      <Style Selector="StackPanel > is:(Control).someClass:pointerover">
          <Setter Property="Margin" Value="0 0 1 4"/>
      </Style>
      <Style Selector="Button">
         <Setter Property="Template">
            <ControlTemplate>
               <ContentPresenter 
                    Name="PART_ContentPresenter"
                    Background = "{TemplateBinding Background}"
                    TextBlock.Foreground = "{TemplateBinding Foreground}"/>
            </ControlTemplate>
         </Setter>
      </Style>
    </Window.Styles>
</Window>

[robloo]

The “Blazor” syntax is a really cool concept too. https://github.com/microsoft/microsoft-ui-xaml/issues/2499 “Proposal: Support Blazor Syntax”

The link to the video where some ideas were presented today by the Uno Platform is below (time 56:14) https://youtu.be/TeS4rX3i_Ls?t=3374

Yes, I’m seeding this all over the place because it’s awesome!

[TonyHenrique]

I prefer the XAML syntax.