The <alert> segmentprovides basic information about the current message: its purposeits source and its status. It also has a unique identifier for themessage and links to any other related messages. An <alert> segmentcan be used alone for message acknowledgments cancellations or othersystem functions; however most alert segments include at least one <info> segment.

The <info> segmentdescribes an anticipated or actual event in terms of urgency (thetime available to prepare) severity (the intensity of the impact)and certainty (confidence in the observation or prediction). It alsoprovides both categorical and textual descriptions of the subjectevent. The <info> segment might also provide instructionsfor appropriate response by message recipients and other detailsfor example hazard duration technical parameters contact informationand links to additional information sources. Multiple <info> segmentscan be used to describe differing parameters such as different probabilityor intensity bands or to provide the information in multiple languages.

The <resource> segmentprovides an optional reference to additional information related tothe <info> segment. It might reference a digitalasset such as an image or audio file.

The <area> segmentdescribes a geographic area to which the <info> segmentapplies. Textual and coded descriptions (such as postal codes) aresupported but the preferred representations use geospatial shapespolygons and circles and an altitude or altitude range expressedin standard latitude longitude and altitude terms in accordancewith a specified geospatial datum.