XML / XSD / XSLT / XAML resources don't go through the C# decompiler so the
DecompilerTabPageModel has no pre-collected foldings — only HighlightingService
was kicking in. Run AvaloniaEdit's bundled XmlFoldingStrategy when the active
syntax extension is .xml so multi-line elements collapse from the gutter.
Assisted-by: Claude:claude-opus-4-7:Claude Code