class ReverseMarkdown::Cleaner

def preserve_border_whitespaces(string, options = {}, &block)
  return string if string =~ /\A\s*\Z/
  default_border = options.fetch(:default_border, '')
  # If the string contains part of a link so the characters [,],(,)
  # then don't add any extra spaces
  default_border = '' if string =~ /[\[\(\]\)]/
  string_start   = present_or_default(string[/\A\s*/], default_border)
  string_end     = present_or_default(string[/\s*\Z/], default_border)
  result         = yield
  string_start + result + string_end
end