What should a generic emotion markup language be able to represent?
Working with emotion-related states in technological contexts requires a standard representation format. Based on that premise, the W3C Emotion Incubator group was created to lay the foundations for such a standard. The paper reports on two results of the group's work: a collection of use cases, and the resulting requirements. We compiled a rich collection of use cases, and grouped them into three types: data annotation, emotion recognition, and generation of emotion-related behaviour. Out of these, a structured set of requirements was distilled. It comprises the representation of the emotion-related state itself, some meta-information about that representation, various kinds of links to the "rest of the world", and several kinds of global metadata. We summarise the work, and provide pointers to the working documents containing full details.