This documentation is not using the current rendering mechanism and is probably outdated. The extension maintainer should switch to the new system. Details on how to use the rendering mechanism can be found here.
Re-using existing fields¶
In most cases the tt_content table (where content elements are stored) contains enough fields to build a content element from. In the core file typo3/sysext/frontend/Configuration/TCA/tt_content.php all the fields of tt_content are configured. Some of the fields are for internal use by TYPO3 CMS, but many are meant for specific content element types and can easily be used by our custom content element.