The Yorkshire Terrier is a small dog breed of terrier type, developed in the 19th century in the county of Yorkshire, England to catch rats in clothing mills. The defining features of the breed are its size, 3 pounds (1.4 kg) to 7 pounds (3.2 kg), and its silky blue and tan coat. The breed is nicknamed Yorkie and is placed in the Toy Terrier section of the Terrier Group by the Fédération Cynologique Internationale and in the Toy Group or Companion Group by other kennel clubs, although all agree that the breed is a terrier. A popular companion dog, the Yorkshire Terrier has also been part of the development of other breeds, such as the Australian Silky Terrier.For adult Yorkshire Terriers, importance is placed on coat colour, quality, and texture. The hair must be glossy, fine, straight, and silky. Traditionally the coat is grown-out long and is parted down the middle of the back, but "must never impede movement." From the back of the neck to the base of the tail, the coat should be a dark gray to a steel-blue, and the hair on the tail should be a darker blue. On the head, high chest, and legs, the hair should be a bright, rich tan, darker at the roots than in the middle, that shades into a lighter tan at the tips. Also, in adult dogs, there should be no dark hairs intermingled with any of the tan coloured fur.