Attributes are useful in precisely such circumstances.
These specify the name of the attribute, the type of value it takes, and a default value respectively. Sometimes, of course, the set of possible values cannot be pre-defined. Where it can, as in this case, it is generally better to do so. Only the status of the first poem need therefore be supplied, if all are the same. Note that not every poem need carry an id attribute and the parser may safely ignore the lack of one in those which do not.