Alloy <Include>

index.xml

<Alloy>
    <Window>
        <Button/>
        <Include src="viewInclude"/>
    </Window>
</Alloy>

viewInclude.xml

<Alloy>
    <View>
        <Label/>
        <Button/>
        <Label>
        <ImageView/>
    </View>
</Alloy>

x_generated.xml

<!--
  Notes:
  - IDs must be managed by developer. Conflicts are possible. We can show warnings/errors if need be.
  - This all happens at compile time.
  - Nested <Include> tags are handled appropriately.
-->
<Alloy>
    <Window>
        <Button/>
        <View>
            <Label/>
            <Button/>
            <Label>
            <ImageView/>
        </View>
    </Window>
</Alloy>