Apply additional constraints for DITA 1.3
Constraints allow you to limit the elements or attributes that can be used in certain contexts. For example, you might want to prevent the use of refsyn and related elements in reference topics. If you don't need to use those elements, you can constrain to simplify the authoring experience for authors. Constraints enable you to use a subset of the structure allowed by the DITA standard in a given context; you cannot use constraints to enable use of structure that the DITA standard itself does not allow.
CAUTION: Be very careful with this change. If you activate the constraints
in CompanyDitabase.dtd after you already have content that references it,
that content might becomes invalid if it uses elements that are no longer allowed
due to the new constraints. You must either edit the content so that it is no longer
invalid or you must edit it so that it no longer references
CompanyDitabase.dtd. The former is obviously the recommended option. To
avoid creating this situation, IXIASOFT strongly recommends making these decisions
before you accumulate a large amount of content.