Custom report items (CRIs) are supported in all Viewers and all types of exports. However, they are not currently supported in the WebDesigner component.
With a CRI, you can implement the following tasks:
To implement a simple CRI, see the RadarChart.cs file in the CustomChart sample to have an idea of what your CRI implementation should look like. If you require access to data, then you should use the IDataRegion interface.
To implement the Designer, see the RadarDesigner.cs file in the CustomChart sample. Remember that the DataSet is required only in case of data binding (the IDataRegion interface). Otherwise, you can use just a simple property that is passed and obtained from a CRI as ReportItem.CustomProperties.
You should also remember to add a configuration file - you can find an example in the CustomChart sample.