The event handler receives an argument of type BeforeExportEventArgs containing data related to this event.
You can check the DevExpress.XtraRichEdit.API.Native.Document.RequiredExportCapabilities to be sure that the chosen export format supports them.
The BeforeExport event enables you to adjust the exporter options as required.
For RTF format, you can specify the DevExpress.XtraRichEdit.Export.RtfDocumentExporterCompatibilityOptions.DuplicateObjectAsMetafile property. For the HTML format, set the location of external content (images, css files) via the DevExpress.Office.Export.IExporterOptions.TargetUri property and specify other DevExpress.XtraRichEdit.Export.HtmlDocumentExporterOptions.