To add to the stress. Think about this: At the moment, you have no need for a nested object selection and you may never. Anyhow, all of a sudden you have a need for a selection of an object or a user other than yourself gets ahold of your code and starts using it. If he selects a nested object, the code could very well be set and ready to go. However, if you don't have the ability to grab a nested object, your user is most likely going to come up to you one day complaining about how that "Killer" app you asked him to use isn't working. You want to tell him that it's probably because he selected an object that he shouldn't be selecting, except Mark can tell you all about how you should never blame your users for selecting objects they shouldn't. If you expect that someone else might use your code, you should have checks and balances built into it, so that if your users pick something they shouldn't they are either told they need to select a different object or allow them the option to exit out safely. The nentsel and *(ssget ":SN" '((0 . "*POLYLINE"))) will ensure that nested selected items can still get processed or their lists can still be collected. It's just nice to have failsafes for such occasions. I know there are times when you really just don't need to care, but you never know.
*Not sure if I got the ":SN" in there correctly. That can be a tricky filter at times. S=single object selection mode and N=nested object selection. If I remember correctly, you can combine them as I've shown and you should be able to only select one nested object as long as you select an object.