We describe a grammatical formalism based on tree descriptions and develop a constraint-based treatment of parsing in that framework. We introduce the language of electrostatic tree descriptions to write lexical entries: these are tree descriptions using neutral, as well as positively and negatively charged variables. We develop an appropriate notion of model. We then extend the framework to disjunctive systems of electrostatic descriptions, and we correspondingly extend the notion of model. Then we show how the search for minimal models can be realized by reduction to a CSP solvable by constraint programming and we provide the full encoding in an axiomatic style.