Description: Optional, if present, specifies that this is a summary alert, representing one or more alerts with common characteristics. The numeric value indicates the number of times the signature fired since the last summary alert with a matching 'initialAlert' attribute value. The first and all subsequent summary alerts in a sequence will use the eventId of a previous non-summary evAlert in the initialAlert attribute value. All alerts represented by the summary alert share the same signature and sub-signature id. The summaryType attribute defines the common characteristic(s) of all alerts in the summary. The 'final' attribute indicates whether this is the last evAlert containing the same value in the 'initialAlert' attribute. The 'final' attribute may be omitted if and only if its value is false.