xml2 vs XMLFunctions

Hi,

I am currently using xml2 functionality in PostgreSQL 8.3.x and want to
substitute it by the newer API as mentioned here:

>From PostgreSQL 8.3 on, there is XML-related functionality based on the
SQL/XML standard in the core server. That functionality covers XML syntax
checking and XPath queries, which is

>what this module does, and more, but the API is not at all compatible. It
is planned that this module will be removed in PostgreSQL 8.4 in favor of
the newer standard API, so you are

>encouraged to try converting your applications. If you find that some of
the functionality of this module is not available in an adequate form with
the newer API, please explain your

>issue to pgsql-hackers(at)postgresql(dot)org so that the deficiency can be
addressed.

The only function of xml2 I ever used was "xpath_bool(document,query)
returns bool" where document represents a table column. How can I do this
with the new API ?

I thought that "9.14.2. Processing XML: xpath(xpath, xml[, nsarray])" might
be the right function, but I don't know how to specify the column where the
xml is stored.

Can you please give me an example ? I only have to implement xpath functions
that return Boolean. I'd like to query - SELECT foo FROM bar AS x WHERE
xpath('xpath', x.xmlcolumn [,nsarray])

Cheers, Tobias