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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _format_envvar(param):
 """Format the envvars of a `click.Option` or `click.Argument`."""

    yield '.. envvar:: {}'.format(param.envvar)
    yield '   :noindex:'
    yield ''
    if isinstance(param, click.Argument):
        param_ref = param.human_readable_name
    else:
        # if a user has defined an opt with multiple "aliases", always use the
        # first. For example, if '--foo' or '-f' are possible, use '--foo'.
        param_ref = param.opts[0]

    yield _indent('Provide a default for :option:`{}`'.format(param_ref))