is operator field in journey structure mandatory or optional?

[matkoniecz]

most fields in https://github.com/public-transport/friendly-public-transport-format/blob/master/spec/readme.md#journey are described as mandatory or optional.

operator field is unspecified

[matkoniecz]

I can make PR after confirmation that this field was supposed to be optional.

[matkoniecz]

I made it anyway, before confirmation.

[juliuste]

Sorry for being so late to comment, IMHO we should be consistent with the decision to make operator required/optional, e.g. also in line.operator. I personally would rather have it required, @derhuerst @matkoniecz @ialokim opinions?

[matkoniecz]

Personally I would prefer it optional, as without it data still makes sense.

I would keep required for things that once missing make data completely useless (like destination or origin).

[juliuste]

We should also decide on #55 while we're at it.