GpaNode------   [duplicate, verify, get_value, set_value, get_child, modified]
  |          |
  |          |- GPANode *parent
  |          |- GPANode *next
  |
  |
  GPARoot----
  |          |- GPANode *vendors
  |          |- GPANode *printers
  |          |- GPANode *media
  |
  GPAVendor--
  |          |- GPANode *name
  |          |- GPANode *url
  |          |- GPAList *models
  | 
  GPAList----
  |          |
  |          |- GPANode *children
  |          |- GPANode *def
  |          |- GType childtype (what is this?)
  |
  GPAReference [set_value (?)]
  |          | 
  |          |- GPANode *ref
  |
  GPAOption--    [create_key]
  |          |
  |          |- GPANode *name
  |          |- GPANode *children
  |          |- GPAOptionType type ----- (NONE, NODE, KEY, LIST, ITEM, STRING)
  |          |- guchar * value
  |
  GPAKey----
  |         |
  |         |- GpaNode *children
  |         |- GpaNode *option
  |         |- guchar *value
  |
  GPAConfig-
  |         |
  |         |- GPANode *globasl
  |         |- GPANode *printer
  |         |- GPANode *settings
  |
  |