class_docstr: A container which simply calls the appropriate methods on the
  contained :class:`RasterSource`.
code: def fetch_raster(self, projection, extent, target_resolution):
      return self._source.fetch_raster(
          projection, extent, target_resolution
      )
  
imports: import collections
  from pathlib import Path
  import string
  from urllib.request import urlopen
  import warnings
  from cartopy import config
label_desc: Use image node_id 2 for calling the RasterSourceContainer obj's underlying member method code with example usage: obj.fetch_raster(projection, extent, target_resolution) and returns: self