dotnet-multi-targetinglisted

# dotnet-multi-targeting Comprehensive guide for .NET multi-targeting strategies with a polyfill-first approach. This skill consumes the structured output from [skill:dotnet-version-detection] (TFM, C# version, preview flags) and provides actionable guidance on backporting language features, handling runtime gaps, and validating API compatibility across target frameworks. ## Scope - Decision matrix: polyfill vs conditional compilation - PolySharp for compiler-synthesized polyfills - SimonCropp/Polyfill for BCL API backporting - Conditional compilation with TFM-based preprocessor symbols - Multi-targeting .csproj patterns and TFM-specific source files - API compatibility validation (EnablePackageValidation, ApiCompat tool) ## Out of scope - TFM detection logic -- see [skill:dotnet-version-detection] - Version upgrade lane selection -- see [skill:dotnet-version-upgrade] - Platform-specific UI frameworks (MAUI, Blazor) -- see respective framework skills - Cloud deployment configuration Cross-references: [skill:dotnet-version-detection] for TFM resolution and version matrix, [skill:dotnet-version-upgrade] for upgrade lane guidance and migration strategies. --- ## Decision Matrix: Polyfill vs Conditional Compilation Use this matrix to select the correct strategy for each type of gap between your highest and lowest TFMs. | Gap Type | Strategy | When to Use