DesignerBuilderType Class
Contains references to builders for a design application compatible with Microsoft SharePoint Foundation, such as SharePoint Designer.
Namespace:
Microsoft.SharePoint.WebPartPages
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
Available in Sandboxed Solutions: Yes
Available in SharePoint Online
When a Web Part is hosted in a design application that supports Web Part builders and a builder is selected on the Property sheet, the window.external.InvokeBuilder method will call the design application and pass the BuilderType, BuilderArguments, and the ElementID information.
The fields of the DesignerBuilderType class are passed to the HtmlEditorBuilderType property.