The Yorkie comes from the crossing of 4 English Terrier breeds and were developed for catching rats and mice. They have a delicate trachea and a harness may be more suited for them.  They can snort, which is called a pharyngeal gag reflex. They have a long coat of hair with no undercoat, so they don't shed.

This little dog has a high energy level and is loyal and a wonderful companion.  He is affectionate. It can be a yapper because owners allow this little dog to get away with things a normal dog would not. He can easily take over the house and become demanding.  Yorkies are easy to train though and can be an excellent watch dog.  When the owners show who is boss, this terrier is very sweet. The problems only happen because of the dogs cute little size, allowing him to get away with things.  

If your Yorkie zooms around the house, it is a sign that you need to walk him more. 
Regular grooming is needed. His hair keeps growing and you need to comb and brush it so it will not get matted.