When the D地i created the original link to an Age, it was done through the writing of a Descriptive Book. This Book was written with all of the descriptions of the Age to which it would link. The Descriptive Book is the primary Book defining a particular Age. The Descriptive Book is a requirement to create the founding link to any Age.
The manuscripts state that the D地i believed that when the writer of an Age describes the Age, the Age is not actually created, but a link is established to a preexisting Age that most closely represents what has been written. The D地i believed that all Ages were actually created by the Maker, and that the D地i were imbued with a gift from the Maker to create links to the Ages.
As far as D地i manuscripts are concerned, Descriptive Books are always written in the D地i language, and always have been. It is not at all clear whether or not other languages could be used. There is some question as to whether there is enough room in a single Book for other languages to describe worlds that the complex D地i characters handle routinely.
Written contradictions in the Descriptive Books were a cause for great concern for the D地i. From a young age, Guild students were taught to concern themselves with the details of what is described in a particular Descriptive Book, so as to avoid contradicting those details later on in the Book. Such contradictions could cause severe instabilities in an Age. D地i culture is fraught with stories of contradictions discovered only after the preliminary scouts from the Maintainers Guild never returned. Such stories were used to impact young writers.
There are a few ancient manuscripts that document making changes to Descriptive Books and their associated Ages once the Ages had been visited. The procedure required meticulous attention to detail and was attempted by only the highest levels of writers. The problem seemed to lie in the synchronization of what was written in the Descriptive Book and what was actually observed on the Age itself. If changes were written into the Book that contradicted previously observed features of the Age, it was possible that the Descriptive Book would divert its link to an Age that more closely resembled the changes described. It would appear that the link to the "pre-diverted" Age would be lost, and it would be impossible to reestablish the original link.
At some point in their history, the D地i seem to have banned the practice of altering Ages once they had been approved by the Guild of Maintainers. More recent manuscripts show that they were very opposed to the risks inherent in attempting to alter an Age
There have been some restrictions discovered regarding writing bizarre Ages, Ages that would defy the laws of nature as the D地i knew them. It seems this is to discourage Books that might create links to unstable Ages.
Restrictions have also been discovered concerning man-made objects written into an Age. It appears that some kind of initial experimentation by the D地i was unsuccessful and unpredictable, and the restriction was established.