Making custom modifications to output HTML

By assigning custom handlers to the OnBeforeFiltering and OnAfterFiltering events, you can make changes to the output HTML code. The events must be connected to the processing of the requests on which you want to make the modifications.

Note: Output customizations can significantly affect site performance.

Assign a handler to the OutputFilterContext.CurrentFilter.OnBeforeFiltering or OnAfterFiltering event.

  • The example uses a custom module class to register the event handlers.
  • The example makes use of the PostMapRequestHandler.Execute event to create an output filter instance on every request.

using System;

using CMS;
using CMS.DataEngine;
using CMS.Base;
using CMS.OutputFilter;

// Registers the custom module into the system
[assembly: RegisterModule(typeof(OutputFilteringModule))]

public class OutputFilteringModule : Module
    // Module class constructor, the system registers the module under the name "CustomOutputFiltering"
    public OutputFilteringModule()
        : base("CustomOutputFiltering")

    // Contains initialization code that is executed when the application starts
    protected override void OnInit()

        // Ensures that the an output filter instance is created on every request
        RequestEvents.PostMapRequestHandler.Execute += PostMapRequestHandler_Execute;

    private void PostMapRequestHandler_Execute(object sender, EventArgs e)
        // Creates an output filter instance

        // Assigns a handler to the OutputFilterContext.CurrentFilter.OnAfterFiltering event
        OutputFilterContext.CurrentFilter.OnAfterFiltering += CurrentFilter_OnAfterFiltering;

    private void CurrentFilter_OnAfterFiltering(ResponseOutputFilter filter, ref string finalHtml)
        // Process the resulting HTML

Each request will now be processed and the output HTML will be modified by the CurrentFilter_OnAfterFiltering method.