where is the RSS 2.0 spec?

The RSS 2.0 specification can be found at the following URL:

https://cyber.harvard.edu/rss/rss.html

This is the official specification for RSS 2.0, which was published by Harvard Law School's Berkman Center for Internet & Society. It provides a detailed description of the elements and attributes that make up the RSS 2.0 format, as well as guidelines for creating valid RSS feeds.