Because the DOM supports navigation in any direction (e.g., parent and previous sibling) and allows for arbitrary modifications, animplementations implementation must at leasttypically buffer the document that has been read so far (or some parsed form of it).<ref>{{Cite book|url=https://books.google.com/books?id=HuSQGrRY7F4C|title=Ajax Black Book, New Edition (With Cd)|last=Kogent Solutions Inc.|publisher=Dreamtech Press|year=2008|isbn=978-8177228380|pages=40}}</ref>. However, a DOM need not originate in a serialized document at all, but can be created in place vi the DOM API. Also, there have been implementations even before DOM itself, of equivalent structure with persistent disk representation and rapid access, such as [[DynaText]]<ref>{{cite patent| country = USA| number = 5557722A| invent1 = Steven DeRose| invent2 = Jeffrey Vogel| status = Expired| title = Data processing system and method for representing, generating a representation of and random access rendering of electronic documents | pubdate = 1996-09-17}}</ref>
