code: def _load_from_environ(metadata, value_func=None):
      
      # We'll match the ennvar name against the metadata's name. The ennvar
      # name must be uppercase and hyphens in names converted to underscores.
      #
      # | envar       | name    | matches? |
      # +-------------+---------+----------+
      # | FOO_BAR     | foo     | yes      |
      # | FOO_BAR     | bar     | no       |
      # | foo_bar     | bar     | no       |
      # | FOO_BAR_BAZ | foo_bar | yes      |
      # | FOO_BAR_BAZ | foo-bar | yes      |
      # +-------------+---------+----------+
  
      prefix = metadata.name.upper().replace("-", "_")
  
      return expand_config(
          environ,
          separator="__",
          skip_to=1,
          key_parts_filter=lambda key_parts: len(key_parts) > 1 and key_parts[0] == prefix,
          value_func=lambda value: value_func(value) if value_func else value,
      )
docs: Load configuration from environment variables.
  
      Any environment variable prefixed with the metadata's name will be
      used to recursively set dictionary keys, splitting on '__'.
  
      :param value_func: a mutator for the envvar's value (if any)