In most situations, specifies whether a duplicate version of the topic is created when it is transformed. This duplicate version can be either literal or virtual. The value of the @copy-to attribute specifies the uniform resource identifier (URI) by which the topic can be referenced by a @conref attribute, <topicref> element, or <xref> element. The duplication is a convenience for output processors that use the URI of the topic to generate the base address of the output. The @keys and @keyref attributes provide an alternative mechanism; they enable references to topics in specific-use contexts without making copies.

The @copy-to attribute also can be used to specify the name of a new chunk when topics are being chunked; it also can be used to determine the name of the stub topic that is generated from a <topicref> element that contains a title but does not specify a target. In both of those cases, no duplicate version of the topic is generated.

For information on how the @copy-to attribute can be used with the @chunk attribute, see Chunking.