When building a room, the builder is given an option of adding what is called an "extra". An "extra" is a thing that people can look at, or examine.

For instance, I have as part of a room description:

The shelf has a number of books on it.

For the 'extra' I could use the keyword "books" and provide a description for the books, such as:

There are a total of seven books of varying sizes. All of the books are bound well and appear to be used little, as indicated by the thick layer of undisturbed dust that has gathered over the years.