What is action filters in ASP.NET MVC?

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http://www.asp.net/mvc/tutorials/older-versions/controllers-and-routing/understanding-action-filters-cs

An action filter is an attribute that we can apply to on top of controller or controller 's action method. This is used to modifies the way of calling of action method. Action filter code run before or after the execution of action method. Action filter represents a cross-cutting concern to our action method.