Redmine

Hi everybody!
I was thinking about purchasing a Reporter plugin from RedmineUp (not advertising, not sure myself that we need it). They are using Liquid markup language to work with different Redmine variables like spent_time_group[0] and status_change.status. When I asked their support where can I get full list of all available variables, they told me to address Redmine. So, here I am :) Anybody knows where to get this list or has one already?

Thanks,
Ihor.