The Delphi form designer uses an interesting control for properties too complex to be efficiently edited with standard property lists: it has what appears to be a normal TEdit linked to a button whose caption is '...'. Pressing this button brings up a custom property editor.

I've seen this TEdit-and-...-button combo in other programs too, used for similar purposes, but I can't find it in the tool palette. I think I must be overlooking it somewhere. What's it called and how do I access it?