For lex mercatoria material on the informality principle:
http://tldb.uni-koeln.de/TLDB.html
Click TLDB's "List of Lex Mercatoria Principles".
"Contractual declarations are valid even when they are not evidenced in writing."
The TLDB database provides annotations to this text. The TLDB annotations address Doctrine, Principles/Model Laws, Conventions, National Legislation.
Pace Law School
Institute of International Commercial Law - Last updated January 28, 2003