class_docstr: A container which simply calls the appropriate methods on the
  contained :class:`RasterSource`.
code: def validate_projection(self, projection):
      return self._source.validate_projection(projection)
  
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 3 for calling the RasterSourceContainer obj's underlying member method code with example usage: obj.validate_projection(projection) and returns: self