when to use custom control and when to use user control?

I am just learning how to write my own controls
here is a statment I read from textbox..


When to use a custom control
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You should use a custom control only if there is some compelling reason for not use a user control.
In the days of the ASP.NET 1.0 and 1.1, there were several benefits to using custom controls compared to user controls


Custom controls had a design-time interface and could be shared among projects,
for instance. However, with Asp.Net 2.0 some of those differences have gone away.
with Asp.net 2.0 there are only three reasons that might cause you to consider using a custom controls;
1 you should use a custom control whenever the control will be used in more than one project
2 you should use a custom control when ...