There are a number of different server tags (<%, <%#, <%$, <%@, <%=) which each mean different things.

This article goes into a little depth talking about each of these tags.

The one I never use, is <%$, which I learned is for displaying expressions, but you can also easily write your own expression provider by extending the expressionbuilder class.  An example of doing so can be found here.

Pretty cool.