A "viewing" is a time when the body is present and friends and family can come and say last farewells. "Visiting hours" are usually a set time when friends and family can gather to commiserate and share recollections of the dead person's life. The body may or may not be present at "visiting hours." Once, bodies were kept at home and the life of the family continued around the dead. Now, it is much more common for the body to be at a funeral home. Even with cremations, the visiting hours are often at a funeral home. Families can arrange these things in other ways, but they usually are willing to do whatever the funeral home director makes readily available.
Those who come to see family and say their farewells will usually be expected to sign a guest book, to approach the body if it is present, and to speak as appropriate to the closest friends and family. Some traditions are more rigid or more openly emotional, but one can usually see those variations fairly quickly. Usually visitors can count on being forgiven for a certain awkwardness, and being gratefully received in the community of the bereaved. It is hard to offend anyone if you are trying charitably to share in grief.
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