Entity Redeclaration in Module Implementation as a DTD

I have two questions;

Firstly, 

I want to know where "NS.prefixed" and "NS.decl.attrib" were defined.

Secondly, 

As you say, Section 4.2 (Entity Declarations) of the XML Recommendation [1] says:
"If the same entity is declared more than once, the first declaration encountered is binding".

I want to know if the next example does not have any problem in redeclaration.

It shows an example of using a different XML namespace prefix in a document instance. 
As you know, the initial value of parameter entity for prefix was set to "inventory" 
in the case of prefixed mode.

<!DOCTYPE i:shelf SYSTEM "inventory-1.dtd" [
    <!ENTITY % Inventory.prefixed "INCLUDE">
    <!ENTITY % Inventory.prefix "i">
]>
<i:shelf xmlns:i="http://www.example.com/xmlns/inventory">
    <i:item>
        <i:desc>
          this is a description.
        </i:desc>
        <i:sku>
          this is the price.
        </i:sku>
        <i:price>
          this is the price.
        </i:price>
    </i:item>
</i:shelf>

Hope your comments,

Jin.