Add new tags to DITA file

[BeeWorker]

I'm starting with DITA technology. I have read about the basic structure of a DITA document. Now, I doubt arises as follows:How can I add my own tags to a DITA document?, Should I create a .DTD file based on a topic.dtd like http://docs.oasis-open.org/dita/v1.2/cd03/dtd1.2/base/dtd/basetopic.dtd?Regards!