ASP.NET automatically evaluates expressions during page parsing using the System.Web.Configuration.ExpressionBuilder class. The System.Web.Configuration.ExpressionBuilderCollection collection, which is made up of the expressionBuilders elements contained in the compilation section of the configuration. The System.Web.Configuration.ExpressionBuilder contains specific values in key/value pairs.

A value is retrieved by including an expression of the form

<%$ ExpressionPrefix: ExpressionKey %>

within the page. The ExpressionPrefix maps the type of expression to be retrieved as either a common expression-builder type (that is, System.Web.Compilation.AppSettingsExpressionBuilder) or a custom expression builder type. The ExpressionKey specifies the key used to reference the returned value.

If you choose to implement a common expression-builder type, you must map the expression builder to the associated section name in the configuration. If you choose to implement a custom expression-builder type, you must map your expression builder to your custom expression-builder class, which must derive from the System.Web.Configuration.ExpressionBuilder class.

Namespace: System.Web.Configuration
Assembly: System.Web (in System.Web.dll)
Assembly Versions: 2.0.0.0
Since: .NET 2.0