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The Winterthur Museum is a collection and a house. There are many museums devoted to the decorative arts and many house museums, but rarely in the United States is a great collection displayed in a great country house. Passing through successive generations of a single family, Winterthur has been a private estate for more than a century. Even after the extensive renovations made to it between 1929 and 1931, the house remained a family residence. This fact is of importance to the atmosphere and effect of the museum. The impression of a lived- in house is apparent to the visitor: the rooms look as if they were vacated only a short while ago whether by the original owners of the furniture or the most recent residents of the house can be a matter of personal interpretation. Winterthur remains, then, a house in which a collection of furniture and architectural elements has been assembled. Like an English country house, it is an organic structure; the house, as well as the collection and manner of displaying it to the visitor, has changed over the years. The changes have coincided with developing concepts of the American arts, increased knowledge on the part of collectors and students, and a progression toward the achievement of a historical effect in period- room displays. The rooms at Winterthur have followed this current, yet still retained the character of a private house.

The concept of a period room as a display technique has developed gradually over the years in an effort to present works of art in a context that would show them to greater effect and would give them more meaning for the viewer. Comparable to the habitat group in a natural history museum, the period room represents the decorative arts in a lively and interesting manner and provides an opportunity to assemble objects related by style, date, or place of manufacture.

What does the passage mainly discuss?

The pronoun "it" in paragraph 2 refers to _____