Is the RFID chip in e-passports read-only or is it read-write? 

If it's read-only, is all of the data locked-down when the passport is issued? Is the read-only portion extensible so that additional data can be burned on later?

If it's read-write, can passport country in any country we pass through enter or change data in the passport? For example, to record entries and departures? 

> Update: I ask for two reasons. The first is that the only biometric I recall giving when I applied for my passport is my photo and I wanted to know if my government could add other biometrics (iris scan, fingerprints) at a later date — either beknownst to me or surreptitiously at a border station. #tinfoilhat
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> Second, I wanted to know if foreign governments could add entry or exit or visa e-tags to my passport, especially when passing through automated gates.