Adding new elements to DocBook...

I am referring to the details available at 
http://www.docbook.org/docs/howto/#customconsiderations for adding new 
elements to the docbook.

Question 1:
What are inline elements? Example 5 
(http://www.docbook.org/docs/howto/#ex-add-element-2) talks about adding 
new inline elements.
Are those different from normal elements?

Question 2: How do I control the number of occurrences of an element? 
Can I use tags <oneOrMore> or <zeroOrMore> in the customization file?
What tag should be used if I want an element to appear only "once" in 
the document?

Question 3.  One can define elements with types such as xs:string, 
xs:short, etc. in an XML Schema document (xsd) .What are the equivalent 
types available in DocBook?

Thank you,
Anagha