My purpose is to 
 display a list of page (with MyClass object): this point is
 working well but ...
  
  I want that the user 
 select in my select
list: one page OR nothing.
 The HTML select element
 supports either single selection (exactly one
 item selected) or multiple selection (0..*). To
 achieve 0..1 you need
 to have a special item
 "Nothing" with value '' (empty string) and
 in
 order to add this item to a Page
 (actually DatabaseList) property you
 have to
 write a custom displayer. Another solution may be to create
 a
 special page with a MyClass object that
 represents the "nothing" value
 (when selected), but you still need to hack
 something in order to have
 this option
 displayed first.
  
 
Yes thxs I though about "custom display" field.
Then I can use a String type with "custom display" or perhaps with database
list+"custom display"  I can catch HTML rendering of select list  to add my
empty option value line...
Anyway Do you know where is source code of Page type to improve it (IMA view mode must
display a link to the target)?
 
 Do you have an idea, how can I do that?
 
  I 
 found a issue too: my select list list
all page (with
 MyClass object) ... even my Template with MyClass object who
 is hidden.
 Does it behave
 the same with a DatabaseList property? The Page
 property is nothing more than a wrapper for the
 DatabaseList property. 
 
Yes it is the same: I just tested. hidden filter is not applied (of course I checked that
user preference is "don't show hidden doc")
Do you know where is query to check it?