How block generation works
How many transactions may be recorded in a single NXT block?
What is its maximum length?
Are there different block structures at different block heights?
How many bytes per tranaction are used? What fields are used to organize these bytes?
From an early post by BCNext:
Address length - 8 B (max 20 chars in human-readable notation)
Private key length - 32 B
Public key length - 32 B
Signature - 64 B
Block header length - 192 B
Transaction length - 128 B
Each transaction has "deadline" value to limit time it can be added into a block. Days when you send a transaction and wait a whole day to get it confirmed have gone for good. Now you can set deadline to 5 minutes and if it's not confirmed then resend it with a higher fee. Also each transaction can be marked with "id" (8 B length) to help merchants to identify your payment. Not necessary to create a separate address for each customer anymore.
(Can someone fill in details like e.g. what is the format of the header and transaction? And this was for an early version, have things changed, are there any other fields?)