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+# Contributing
+
+RETRO is an open-source project, but I am opinionated, and as I am
+developing this primarily for my use, I may be picky when it comes
+to adding changes to the core language.
+
+I use Fossil to manage the RETRO source, but I do not accept pushes
+to this directly. Patches or updated files can be emailed to
+crc@forthworks.com. I will review and merge them manually.
+
+## Interfaces
+
+When making changes, I'm most open to extensions as part of the RRE
+interface. (interfaces/rre.c, interfaces/rre.forth).
+
+New interfaces are welcome. If they require more than 1-2 files, or
+specific build systems (apart from BSD compatible `make` or `bin/sh`
+scripts), please keep them in a separate subdirectory.
+
+I'm not planning to accept new I/O or extensions to the basic REPL
+(interfaces/repl.c) as this serves as a template for starting new
+interfaces or implementations.
+
+Changes or additions to the provided words must be documented in the
+glossary (words.tsv).
+
+## Kernel
+
+The kernel (literate/Rx.md) is basically done. I'm still making small
+changes in terms of tuning size/performance, but will not merge any
+alterations to this apart from bug fixes currently.
+
+## Standard Library
+
+I may accept additions to the standard library. Words requiring any
+I/O other than `putc` will not be accepted in the standard library.
+
+Changes to the words must be documented in the glossary (words.tsv).
+
+## Examples
+
+I'm quite willing to add new examples or changes / improvements to
+existing ones.
+
+## Legal
+
+All contributions to the main sources (existing interfaces, kernel,
+standard library) must be public domain or under the ISC license
+(see LICENSE.md). Please add the appropriate copyright notices to
+the LICENSE and/or source files.
+
+New examples or tools can be under similar licenses. Include the
+copyright and license text in the sources.
+
+I will not accept contributions under the GPL, LGPL, AGPL, or other
+licenses that are too long to reasonably embed in a source file.
+
+## Building
+
+I do builds under GCC and CLANG on FreeBSD, NetBSD, Linux, macOS,
+and Haiku. I build RRE for Windows using TCC on a Windows box.
+Changes to the source must build cleanly on all test systems.
+
+Note that Haiku uses GCC 2.95.3 for backwards compatibility with
+BeOS R5 so sources must compile on this as well as modern compilers.