id: identifier (text). Upto March 2007 was archive.subject_class/yearmonthnumber. For example math.GT/0309136.
Since April 2007 YYMM.number
submitter - text
authors - text but use separate file
title - text
comments - text
journal-ref - text
doi - text
abstract - text
report-no - text
categories - list
versions - list