Attributes are in key-value form, and if there's no value provided for an attribute, a NotAvailableValueError will be raised.
# File rss/rss.rb, line 153 def initialize(tag, value, attribute=nil) @tag, @value, @attribute = tag, value, attribute message = "value <#{value}> of " message << "attribute <#{attribute}> of " if attribute message << "tag <#{tag}> is not available." super(message) end