code: def _get_section(name, source):
      # type: (str, str) -> Optional[str]
      
      pattern = re.compile(
          '^([^\n]*{name}[^\n]*\n?(?:[ \t].*?(?:\n|$))*)'.format(name=name),
          re.IGNORECASE | re.MULTILINE)
      usage = None
      for section in pattern.findall(source):
          usage = _merge_section(usage, section.strip())
      return usage
docs: Extract the named section from the source.
  
      Args:
          name: The name of the section to extract (e.g. "Usage").
          source: The usage string to parse.
  
      Returns:
          A string containing only the requested section. If the section appears
          multiple times, each instance will be merged into a single section.