DOCBOOK: procedure in article is giving a validation error

Hello,

I have used docbook for the first time today and I am trying to use a
<procedure> within an <article>. I get the following error when trying to
validate:

Element content is invalid according to the DTD/Schema.
Expecting: lot, section, toc, index, glossary, bibliography, appendix,
ackno.

<procedure>
-----------^

Any idea what is wrong? 

PS - I am using the following declaration <!DOCTYPE article PUBLIC
"-//OASIS//DTD DocBook XML V4.1.2//EN"
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd">

tamuch

V