def []=(attr, value)
      raise "argument to [] must be a Symbol or a String." unless attr.is_a?(Symbol) or attr.is_a?(String)
      @attributes = { } if !instance_variable_defined?(:@attributes) or @attributes.nil?
      @attributes[attr] = value.to_s
    end
def []=(attr, value)
      raise "argument to [] must be a Symbol or a String." unless attr.is_a?(Symbol) or attr.is_a?(String)
      @attributes = { } if !instance_variable_defined?(:@attributes) or @attributes.nil?
      @attributes[attr] = value.to_s
    end
Adds or set an attribute of the Instruct.
 - +attr+ [Symbol|String] attribute name or key
 - +value+ [Object] value for the attribute