Do you mean something like a hook_token?
Such a hook can return variables-like tokens. For example:
token_set('site')
and then retrieved the same way with
token_get('site')

The same naming convention can be used here as well: token_set('drupal_site'), token_set('simplenews_unsubscribe_uri') etc.

Is that what you meant?

Zohar



Bèr Kessels wrote: 
Op woensdag 6 december 2006 13:30, schreef Konstantin Käfer:
  
If I understand it correctly, you mean something like this:

- The user has a list of possible values, for example:
    

No, more a general place/code for something like: 
http://example.com/admin/settings/user

Customize the body of the welcome e-mail, which is sent to new members upon 
registering. Available variables 
are: %username, %site, %password, %uri, %uri_brief, %mailto, %login_uri, %edit_uri, %login_url.

This is now hardcoded into user.module. And there are many more flavors and 
concepts that do almost the same, and need to hardcode this.

Bèr