The registry stores data in a hierarchically structured tree. Each node in the tree is called a key. Each key can contain both subkeys and data entries called values. Sometimes, the presence of a key is all the data that an application requires; other times, an application opens a key and uses the values associated with the key. A key can have any number of values, and the values can be in any form.
Each key has a name consisting of one or more printable ANSI characters — that is, characters ranging from values 32 through 127. Key names cannot include a space, a backslash (\), or a wildcard character (* or ?). Key names beginning with a period (.) are reserved. The name of each subkey is unique with respect to the key that is immediately above it in the hierarchy. Key names are not localized into other languages, although values may be.