[web] safety belt to avoid overriding pageid with loadxhtml()
HtmlHeaders.define_var() now accepts a third optional 'override' paramater.
If set to False, the variable won't be evaluated if it's already defined
in the page.
Schema of the data
------------------
First take a look at the data schema_ then try to remember that you are browsing
through a heap of data by applying stylesheets to the results of queries. This
site is not a content management system with items placed in folders. It is an
interface to a database which applies a view to retreived data.
.. _schema: schema