Dragging an xref object to the Tool Palettes window elicits a special response from the framework. An overlay image identifying an xref tool is superimposed on the lower-right corner of the tool's standard image. You can provide an overlay image for any catalog item that you define. The AcTcCatalogItem class provides functions for specifying and querying overlay images.
By default, the framework sizes an overlay according to the tool image's proportions. You can override the default size by specifying an overlay image's dimensions, but the area you specify must be smaller than that of the tool image.