All these publications are explanations of the official spelling rules, as set by the Dutch Language Union.
After the spelling reform of 2005, the White Booklet was updated explicitly in a break with the Dutch Language Union.
[1][2] The latest edition will, because of the changes, be unable to bear the official certification mark of the Dutch Language Union.
These parties have jointly announced in December 2005 that they will not switch to the new official spelling, and they had not done as of August 1, 2006.
Even though Onze Taal is a society for both Belgium and the Netherlands, no major media or publisher in Flanders uses the White Booklet.