I have a custom tool that can generate multiple feature classes. It works for a single feature class if I set the output parameter to a data element feature class, but not for multivalue.
We previously had been using the current ArcGIS application ref to manually add the layers. However, that doesn't work with background geoprocessing. So, we're wondering if there is a prescribed method for this.
I didn't look extensively, but I haven't found an ESRI tool with a multivalue output parameter to test against.