The keys attribute

A @keys attribute consists of one or more space-separated keys. Map authors define keys using a <topicref> or <topicref> specialization that contains the @keys attribute. Each key definition introduces an identifier for a resource referenced from a map. Keys resolve to the resources given as the @href value on the key definition <topicref> element, to content contained within the key definition <topicref> element, or both.

The @keys attribute uses the following syntax:

The value of the @keys attribute is one or more space-separated key names.
Key names consist of characters that are legal in a URI. The case of key names is significant.
The following characters are prohibited in key names: "{", "}", "[", "]", "/", "#", "?", and whitespace characters.

A key cannot resolve to sub-topic elements, although a @keyref attribute can do so by combining a key with a sub-topic element id.

3.17.13.2 The @keys attribute

3.17.13.2 The `@keys` attribute