For information on converting to InterSystems IRIS,
see the InterSystems IRIS Adoption Guide
and the InterSystems IRIS In-Place Conversion Guide,
both available on the WRC Distributions page (login required).
Inherited description: Event handler for PreHTTP event: this is invoked before
the HTTP headers for a CSP page have been sent. All changes to the
%CSP.Response class, such as adding cookies, HTTP headers,
setting the content type etc. must be made from within the OnPreHTTP() method.
Also changes to the state of the CSP application such as changing
%session.EndSession or %session.AppTimeout must be made within the OnPreHTTP() method.
It is prefered that changes to %session.Preserve are also made in the OnPreHTTP() method
as this is more efficient, although it is supported in any section of the page.
Return 0 to prevent OnPage() from being called.