SMTP Actions

Is there a wiki or some document that I can use to help construct the messages that get emailed as an Alert Response?

For example, the initial is as follows:

Subject: SQLDM Alert ($(Severity)) - $(AlertSummary) on $(Instance)

Message:

$(Timestamp), $(Metric) on $(Instance) and host $(Hostname) is $(Severity).

$(AlertText)

I would like to see what else I can add in order to make the messages the most useful.