This paper deals with the incremental interpretation of on-line structured documents. We introduce Context- Driven Constraint Multiset Grammars (CDCMG) to model the analysis of strokes drawn in the context of document composition; they allow visual arrangement, constraint and stroke recognition system handling by coupling a global vision of the document with a local vision of the analyzed elements. The associated incremental parser interprets the hand-drawn strokes and allows immediate feedback to the user. Moreover, we extend CDCMG by exploiting fuzzy logic to take into account the imprecision of handwriting and explain the impact on ambiguity management. Thanks to this approach, pen-based interfaces have been designed; we present and evaluate more specifically a software for electric diagram drawing, both in terms of comparison with more usual button-based interfaces and recognition rates.