The user-defined event handlers always accept a 'control'
parameter whose type is the same as that of the control it belongs
to. For example the on-post event of 'button' has a parameter
'control' of type vspx_button; after-data-bind of a 'label' has a
parameter 'control' of type 'vspx_label' etc.
The event handlers for before-data-bind, after-data-bind and
on-post have an additional parameter: 'e' which is of type
vspx_event. The parameter ('e') keeps the HTTP request as post
data, request header and path just like the global variables
'path', 'params' and 'lines' on a VSP page. In addition to that,
the vspx_event (e) keeps a reference to the button pressed (if any)
and a flag indicating the request type: POST or GET. It may thus be
used in a complex form to detect when to trigger an event depending
of event data or to directly access parameters of the HTTP request,
create type vspx_event
ve_params any, -- name value pairs of post data
ve_lines any, -- HTTP header lines
ve_path any, -- requested path , parsed as vector
ve_button vspx_control, -- which active control originated the event.
ve_is_post int default 0 -- 0 for GET 1 for POST
) temporary self as ref