- High-level what is PSGI:
  - Interface between web app and web server.
  - a specification (not code)

- Why care about understanding PSGI when you can just use a high-level language.

- Alternatives: CGI, mod_perl, FCGI, SCGI, WSGI (Python), JSGI (JS), Rack (Ruby), ISAPI (IIS)

- Describe how CGI, mod_perl, and FCGI work.

PSGI is easy. RFC 3875 (CGI 1.1) is 36 pages.
The PSGI spec is shorter and much more consumable.

Overview of HTTP?

Implementations:
  - Plack
  - Alternatives: Paste (Python), 
  - Rack-compliant: Rack (Ruby), Clack (Common Lisp)

Benefits of PSGI:
- Web frameworks only need to target PSGI.
- Easy to write tests because requests and responses are data, not necessarily bytestreams.

- What frameworks support PSGI?
  - [Catalyst](http://www.catalystframework.org/)
  - [Mojolicious](http://mojolicious.org/)
  - [Dancer](http://perldancer.org/)
  - [CGI::Ex](https://github.com/chazmcgarvey/CGI-Ex/tree/psgi-2)

- What handlers does plack support?

- What types of things should be written as middleware?