How can I find out the code DRIMSeq uses to make dmplotProportions objects? I'm using DRIMSeq to do some analysis but I'd like to make my own figures from the results ideally using what they've done as a base.

I'm trying to find how they make their ggplot objects in the function plotProportoins but when I use findMethods('plotProportoins') it ends up with a method dmPlotProportoins.

It says in the manual that it's a ggplot object but I can't seem to find how they make it. Any ideas?
I was curious how they have done it as well, so here expanded @Liopis comment :

wget http://bioconductor.org/packages/release/bioc/src/contrib/DRIMSeq_1.6.0.tar.gz
tar -zxf DRIMSeq_1.6.0.tar.gz 
# if you need to find it, or use grep
# find DRIMSeq -name "dm_plotProportions.R"
less DRIMSeq/R/dm_plotProportions.R