The System.Web.Compilation.ExpressionPrefixAttribute class is used at design time with expressions that are not defined in the configuration file. Use the ExpressionPrefixAttribute.ExpressionPrefix property to get the name of the prefix that is associated with the System.Web.Compilation.ExpressionPrefixAttribute object. An expression builder looks for any statements with the following form:

<%$ [expressionPrefix]:[expressionValue] %>

Then the expression builder, based on the prefix of the expression, generates code for the property assignment. The expressionPrefix parameter refers to a configured expression builder, which is defined in the configuration file or through an System.Web.Compilation.ExpressionPrefixAttribute object.