This paper presents a scheme for extending an informal, pen-based whiteboard system (Tivoli on the Xerox Live-Board) to provide a structured editing capability without violating its free expression and ease of use. The scheme supports list, text, table, and outline structures over handwritten scribbles and typed text. The scheme is based on the system temporarily perceiving the “implicit structure” that humans see in the material, which is called a WYPIWYG (What You Perceive Is What You Get) capability. The design techniques, principles, trade-offs, and limitations of the scheme are discussed. A notion of “freeform interaction” is proposed to position the system with respect to current user interface techniques.