Step 2-2. Create New Document Type Shell DTD

In the base DITA distribution, find the file "concept.dtd" and copy it into the faq-question/dtd directory and rename it "faq-question.dtd" (in the sample materials this file is named faq-question-v1.dtd).

Edit this file as follows:

Delete the header comments and replace them with your own that indicates this document type shell DTD is owned by you and specific to the FAQ question module.
Remove any references to any domain modules and entity files you don't need. Which ones you need is entirely your decision—if the FAQ is about a software product you may in fact need the software and UI domains. For simplicity you can leave all those declarations alone for now and worry about it later (or let the users of your module worry about it). In the tutorial materials I've used only the highlight and utility domains within this shell.
Find the parameter entity named %concept-info-types; and rename it to %faq-question-info-types;. Set its replacement text to "no-topic-nesting", rather than "%info-types;".
The <no-topic-nesting> element is one of the DITA "specialization" element types that exist to work around limitations in DTD syntax. In particular, if you have a content model declared like so:
```
 (%some-parameter-entity;)
```
You cannot simply set %some-parameter-entity; to an empty string, because the resolved result would be:
```
()
```
which is not valid.
The solution is to define an empty element type that acts as a placeholder, thus <no-topic-nesting>.

Try validating or opening the test document again. This time you should not get a "DTD not found" error but you should get "element type 'faq-question' not declared" sort of errors, indicating that it found the DTD but not the declarations for the FAQ-specific element types, which of course we haven't created yet. But we're making progress.