UnzipFile interface: "occasionally the stream will be enabled even without start() being called"

[valadaptive]

The start() method of the UnzipFile interface says:

Starts reading from the stream. Calling this function will always enable this stream, but ocassionally the stream will be enabled even without this being called.

This is quite vague. I can't tell from reading the source code when exactly this will happen.

If one wants to implement an API where the consumer is given a list of files in a .zip archive and can decide when to unzip them, it's made way more complicated if the files can decide to randomly start streaming themselves.

If zipped files only began streaming when you called start(), I could just store a map of filenames to UnzipFiles, and then begin unzipping each file only when the API consumer asked for it. But if an UnzipFile can start streaming at any point, we need to attach an ondata handler to each file immediately to avoid missing any events, and squirrel away any data that starts streaming early. This is an entire extra code path that may not ever be exercised.

Under what circumstances will an UnzipFile's stream be enabled without us calling start()?