RegEx for matching alternating case letters

Question

I would like to detect the following sequences:

a
aA
aAa
aAaA
...

where a~[a-z] and A~[A-Z], the case alternates and the first letter is always lower-case.

Thanks,
Tom

Answer 1

[a-z]([A-Z][a-z])*[A-Z]?

Answer 2

The regex that @tanascius gave is fine, and based on that, a shorter one could be:

([a-z][A-Z])*[a-z]?

A major difference is that this one will match the empty string. I wasn't sure from the examples if that was allowed.