Content creation screen: Add another field conditionally I'm trying to figure out how to do the following in D7:
I have a list field in a custom content type. The list contains 8 items. When creating content of this content type, the user can only select one item from this list. But there are two items from this list that I would like to have their own sub-lists. How would I have Drupal conditionally show another list if one of these items were selected? (This is all happening on the content creation screen).

Update
This is not a duplicate of the question you have referenced because this is regarding Drupal 7 content creation. The "Conditional Fields" module was built for Drupal 6 and is not fit for production, as per the module page, in Drupal 7 pages. I am looking for a stable, maintainable solution for a production website.
You may want to take a look at the Hierarchical Select module. It provides this kind of functionality for vocabularies.