Poisson constraint for statistical error in HistFactory

Hello, reading the document about HistFactory:

https://cdsweb.cern.ch/record/1456844/files/CERN-OPEN-2012-016.pdf

I see in equation 9 that the constraints on the statistical error of the MC are Poissonian. This is not the case when I simply call:

background.ActivateStatError()

channel.AddSample(background)

measurement.AddChannel(channel)

ws.obj("gamma_stat_channel_bin_1_constraint").Print()

RooGaussian::gamma_stat_channel_bin_1_constraint[ x=nom_gamma_stat_channel_bin_1 mean=gamma_stat_channel_bin_1 sigma=gamma_stat_channel_bin_1_sigma ] = 1

I guess that this is beacuse of this line, which initialize it to be a gaussian constraints.

https://root.cern.ch/gitweb?p=root.git;a=blob;f=roofit/histfactory/inc/RooStats/HistFactory/Systematics.h;h=d1000bc3bad896745b6d711582d9b666e23d9fad;hb=HEAD#l359

Can you:

1. better document or
2. use Poissonian constraints as written in the documentation?