Contributing guide

Documentation/contributing-guide.md

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+# Contributing Guide
+
+Primary focus of .NET Core 3.0 release is to achieve parity with WPF for .NET Framework.
+Since we're currently still porting parts of WPF codebase (incl. tests) to GitHub (see progress at [../README.md#port-status]),
+we're not ready to handle non-trivial or larger contributions beyond parity fixes yet.
+
+We plan to accept these kind of contributions during 3.0 release:
+
+* Low-risk changes, which are easy to review (e.g. typos, comment changes, documentation improvements, etc.).
+* Test fixes, test improvements and new tests increasing code coverage.
+* Infrastructure fixes and improvements, which are aligned with achieving our goal to ship high quality .NET Core 3.0 release.
+* Bug fixes for differences between WinForms for .NET Core and .NET Framework.
+
+If you have a **larger change** falling into any of these categories, we recommend to **check with our team members** prior to creating a PR.
+We recommend to first create a [new issue](https://github.com/dotnet/wpf/issues), where you can describe your intent and help us understand the change you plan to contribute.
+
+**WARNING:** Expect that we may reject or postpone PRs which do not align with our primary focus (parity with WPF for .NET Framework), 
+or which could introduce unnecessary risk (e.g. in code which is historically sensitive, or is not well covered by tests).
+Such PRs may be closed and reconsidered later after we ship .NET Core 3.0.
+
+
+
+## Developer Guide
+
+Before you start, please review [WPF contributing doc](TODO) and **[.NET Core contributing doc](https://github.com/dotnet/corefx/blob/master/Documentation/project-docs/contributing.md)** for coding style and PR gotchas.
+
+* Per-machine setup: [Machine setup](#machine-setup) and [Fork and clone repo](https://github.com/dotnet/corefx/wiki/Checking-out-the-code-repository)
+* [Build and run tests](#build-and-run-tests)
+* [git commands and workflow](https://github.com/dotnet/corefx/wiki/git-reference) - for newbies on GitHub
+* Pick issue: [up-for-grabs](https://github.com/dotnet/wpf/issues?q=is%3Aopen+is%3Aissue+label%3Aup-for-grabs) or [easy](https://github.com/dotnet/wpf/issues?utf8=%E2%9C%93&q=is%3Aopen+is%3Aissue+label%3Aeasy)
+* [Coding guidelines](https://github.com/dotnet/corefx/tree/master/Documentation#coding-guidelines)
+
+### Machine Setup
+
+TODO
+
+### Build and run tests
+
+#### To build
+
+In the root of your repo, run `build.cmd` (or `build.cmd -verbose` for logs).
+
+#### To run tests
+
+In the root of your repo, run `test.cmd` or open the solution file `src\Microsoft.DotNet.Wpf\test\DRT\DrtXaml.sln` ("DRT" is an internal name used for unit tests).
+* Note that this will test the version of `System.Xaml.dll` currently installed in your shared framework; if you rebuild `System.Xaml.dll` and want to test your changes, you will need to replace the current DLL with your own (be sure to make a backup first).