Conditions making 'feed_info.txt' required

### Introduce yourself

I'm Brewenn and I work at French national access point ([transport.data.gouv.fr](https://transport.data.gouv.fr/)). I help data producers to publish and improve the quality of their datasets. I also advice reusers to ease data integration.

Our team has been developping a gtfs validator and so we follow the evolution of standard.

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In [GTFS reference](https://gtfs.org/documentation/schedule/reference/#feed_infotxt), feed_info.txt is 'Conditionally Required' (I believe it was 'optionnal' but maybe it was a long time ago). By reading the 'Schedule' part of gtfs.org, I don't understand what are the conditions making this file required. Do you know where can I find theses informations please?