Declaring the Event
Go Up to Defining Your Own Events
Once you have determined the type of your event handler, you are ready to declare the method pointer and the property for the event. Be sure to give the event a meaningful and descriptive name so that users can understand what the event does. Try to be consistent with names of similar properties in other components.
Event names start with "On"
The names of most events in Delphi begin with "On." This is just a convention; the compiler does not enforce it. The Object Inspector determines that a property is an event by looking at the type of the property: all method-pointer properties are assumed to be events and appear on the Events page.
Developers expect to find events in the alphabetical list of names starting with "On." Using other kinds of names is likely to confuse them.
Note: The main exception to this rule is that many events that occur before and after some occurrence begin with "Before" and "After."