This site is not a normative reference, spelling out all of the various ways that syndicated feeds can be created in compliance with the specifications. Instead it takes a simpler, best practices approach to feed development. This makes it a good starting point to learn RSS and other feed formats as well as a good quick reference to come back to when necessary. If it becomes necessary to deviate from the code and examples here then please consult the original specifications.
Since the various web page and feed formats are XML-based, the syntax rules for XML format files apply to all types of feeds and other web documents.
1) The original specification RSS 2.0 at Harvard Law is available under the Creative Commons Attribution / Share Alike license (version 1.0). Under the "Share Alike" provision of that license, there is a zip archive, in HTML 5 code with line breaks converted to Unix ^J (0x0a) characters, available to download from this site, and since it's licensed under the same Creative Commons license as the original RSS specification from which it was derived, you are free to modify it, as long as you license it on the same terms as which it was licensed to you, and give proper attribution credit. The HTML documents in the original zip archive of the RSS Specification were written using HTML 4.01 Transitional DOCTYPE and the line breaks were ^M (0x0d) characters.