In addition to extending that text, commit 8119bc1 inserted a paragraph break between the description of the "asis" feature and the "Python handlers" feature. The docs now read:

For full control over the request and response, the server provides the ability to write .asis files; these are served as literal HTTP responses. In other words, they are sent byte-for-byte to the server without adding an HTTP status line, headers, or anything else. This makes them suitable for testing situations where the precise bytes on the wire are static, and control over the timing is unnecessary, but the response does not conform to HTTP requirements.

The server also provides the ability to write Python "handlers"--Python scripts that have access to request data and can manipulate the content and timing of the response. Responses are also influenced by the pipe query string parameter.

@foolip do you think that will be enough to prevent confusion?

Yep, that resolves the confusion, thanks @jugglinmike!