Ensemble aggregation on dataset load?

[flicj191]

Hello all,
I have a question as I was struggling to find the documentation/code to confirm, I have found that when I load a Dataset that has multiple ensembles it loads a single cube, which looks like the mean of the ensembles.
Is this correct? Where can I find how it does this?

from esmvalcore.dataset import Dataset
var = Dataset(
    short_name='ts', mip='Amon', project='CMIP6',
    activity='CMIP',  dataset='CESM2',
    ensemble='*',
    institute='*', grid='*',
    exp='historical', timerange='*'
)
# number of datasets and list (11 ensembles)
len(list(var.from_files())), list(var.from_files())
var.load()  # a single cube

I just did a simple plot to check that it looks like the mean:

from esmvalcore.preprocessor import annual_statisitics, area_statistics
import iris.quickplot as qplt
import matplotlib.pyplot as plt

for ds in list(var.from_files()):
    cube = ds.load()
    cube = annual_statistics(cube, 'mean')
    qplt.plot(area_statistics(cube, 'mean'), label=ds['ensemble'], linewidth=0.5)

#do same for var dataset load
cube_var = annual_statistics(var.load(), 'mean')
qplt.plot(area_statistics(cube_var, 'mean'), label=var['dataset'], linewidth=1, color='k')
plt.legend()