The Chapin Library's main attraction is its collection of Revolutionary-era documents, including a 1776 printed version of the Declaration of Independence.
The collection contains among earlier documents Revolutionary-era documents 
The key here is "among earlier documents". No time period stated other Revolutionary-era.
( z1 contain :ARG0 ( z2 collection ) :ARG1 ( z3 document :time ( z4 before ) :prep-among ( z5 document :mod ( z6 era :mod ( z7 revolution ) ) ) ) )