Is it possible to create a list within a list?

Regarding your Side Question:

You can see to what list(s) you've added a title by using the same mechanism that lets you add a title to lists from the title page: the Add to Watchlist dropdown button (on the desktop version of the site), which reveals:

Notice that 2 lists are checked for this title, and there's a scrollbar when you have enough lists to justify it.

Regarding your Idea: Lists within lists.

How does this differ from being able to Refine your list, or use Advanced Title Search on it?

Hey there... my idea is simple and will make lists a bit easy to access.
I started lists with movies that i watch and added  them there, later on I decided to make lists for film series but now all lists are alltogether and looks pretty awful.

The idea is: Allow us to create a folder, and in that folder we can create lists or move lists with the film series (in my case). So when I want to see all film series or someone accidentally bumps into my lists and is like "hey, lets see what film series this dude have here" he can enter on the folder named for example "Film Series" and there will be all lists for those movies.

This way the lists zone in my case will look more nicely and easy to use, will be like, Artistic Movies, Animation Movies, TV Series, Parody Movies & the folder with Film Series. After all is all about esthetics and easy accessibility

Hope I choose the correct topic, there wasnt anything else.

Would like to see ability to create sub lists withing our lists.  And view them as folders and sub folders rather than lists.

Not sure if this is an idea or question