[threeten-dev] Era value

[yoshito_umaoka at us.ibm.com]

This is purely a question - not pointing out any issues in the spec.

The Era#getValue() spec says:

"The era in use at 1970-01-01 must have the value 1...."

I'm wondering if this requirement is really necessary. In some calendar 
systems, there is only one era (well, conceptually, nothing before epoch). 
Of course, we could artificially invent post epoch era as era 0. Also, 
Japanese/Chinese dynasty eras could be over 100. If we use an era 
including 1970-01-01 as era 1, era value could ends up 3 digits negative 
value, which just look awkward.

I was thinking about the reason behind this, but I could not see any 
convincing reasons. Can someone explain why this is a requirement?

Thanks,
Yoshito Umaoka (ICU Project at IBM)