We have created a property using the PropertyList (http://world.episerver.com/blogs/Per-Magne-Skuseth/Dates/2015/11/trying-out-propertylistt/). I tried to add some custom validating to the "Item details"-dialog (http://henrikm.com/custom-episerver-property-validation/) and that works fine, except for the validation is kicking in when the auto save occurs and not when I click Add in the dialog. So I was thinking of another approach; extending the dialog in dojo and do my validation there. I know that we can extend the PropertyList using epi-cms/contentediting/editors/CollectionEditor, but how do I extend the item dialog?