Moving docs from /vX to /docs; we will use branches for old versions.

docs/user-guide/identifiers.md

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+---
+---
+
+All objects in the Kubernetes REST API are unambiguously identified by a Name and a UID.
+
+For non-unique user-provided attributes, Kubernetes provides [labels](/docs/user-guide/labels) and [annotations](/docs/user-guide/annotations).
+
+## Names
+
+Names are generally client-provided.  Only one object of a given kind can have a given name at a time (i.e., they are spatially unique).  But if you delete an object, you can make a new object with the same name.  Names are the used to refer to an object in a resource URL, such as `/api/v1/pods/some-name`.   By convention, the names of Kubernetes resources should be up to maximum length of 253 characters and consist of lower case alphanumeric characters, `-`, and `.`, but certain resources have more specific restrictions.  See the [identifiers design doc](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/design/identifiers.md) for the precise syntax rules for names.
+
+## UIDs
+
+UID are generated by Kubernetes.  Every object created over the whole lifetime of a Kubernetes cluster has a distinct UID (i.e., they are spatially and temporally unique).