This class inherits from the SpatialExperiment (SPE) class,
which in turn inherits from SingleCellExperiment (SCE).
SpatialFeatureExperiment stores geometries of spots or cells in
sf objects which form columns of a DataFrame which is in turn a
column of the int_colData DataFrame of the underlying SCE
object, just like reducedDim in SCE. Geometries of the tissue outline,
pathologist annotations, and objects (e.g. nuclei segmentation in a Visium
dataset) are stored in sf objects in a named list called
annotGeometries in int_metadata.