model-example1.js

var extend = require("util")._extend;


module.exports.example1 = function() {
    return {
        
        characteristics: {

            length: extend(new Char("length"), { 
                validate: validateLength 
            }),

            curvedEdges: extend(new Char("curvedEdges", "single-select"), {
                options: [
                    new CharValue("None", 0),
                    new CharValue("1", 1),
                    new CharValue("2", 2),
                    new CharValue("3", 3)
                ],
                validate: validateCurvedEdges
            }),


        }
    };
};




///// Rules used in the model \\\\\

function validateLength(next) {
    var selection = this.get("selection");
    if (isNaN(selection)) { // only number required
        this.set("valid", false);
        this.set("invalidMessage", "Length must be a number.");
        return next();
    }

    var length = Number(selection);

    if (length < 20) {
        this.set("valid", false);
        this.set("invalidMessage", "Length must be greater or equal to 20.");
        return next();
    }

    if (length > 44) {
        this.set("valid", false);
        this.set("invalidMessage", "Length must be lower or equal to 44.");
        return next();
    }

    return next();
}


function validateCurvedEdges(next) {
    var lengthSelection = this.get("../length/selection");
    var lengthValid = this.get("../length/valid");

    if (lengthValid) {
        var length = Number(lengthSelection);
        if (length > 36) {
            var selection = this.get("selection");
            var options = this.get("options");
            var selectedCurvedEdges = getSelectedOption(selection, options);
            if (selectedCurvedEdges.value === 3) {
                this.set("valid", false);
                this.set("invalidMessage", 
                        "When length is greater than 36, curved edges " +
                        "can not be 3.");
                return next();
            }
        }
    }

    return next();
}



///// Future infernal-framework \\\\\


var charCount = 0;

var charTypes = ["text", "single-select"];


// Creates a new characteristic
function Char(name, type) {

    if (typeof name === "undefined") {
        name = "char" + charCount;
        charCount++;
    }

    if (typeof type === "undefined") {
        type = "text";
    }

    if (charTypes.indexOf(type) === -1) {
        throw new Error("the characteristic type must be one of " + 
                JSON.stringify(charTypes));
    }

    this.name = name;
    this.text = name;
    this.selection = null;
    this.options = [];
    this.valid = true;
    this.invalidMessage = "";
    this.allowNull = true;
    this.visible = true;

    if (type === "single-select") {
        this.validateSelection = validateSingleSelection;
    }
}


// Creates a new characteristic value
function CharValue(name, value) {
    this.name = name;
    this.value = value;
    this.text = value;
    this.available = true;
}

// validate the selection againsts available options
function validateSingleSelection(next) {
    var type = this.get("type");
    if (type !== "single-select") {
        return next();
    }

    var allowNull = this.get("allowNull");
    var selection = this.get("selection");
    if (!selection && !allowNull) {
        this.set("valid", false);
        this.set("invalidMessage", "Empty value not allowed.");
        return next();
    }

    var options = this.get("options");
    var selectedOption = getSelectedOption(selection, options);
    if (!selectedOption) {
        this.set("valid", false);
        this.set("invalidMessage", 
                "The selection is not found in options.");
        return next();
    }

    if (!selectedOption.available) {
        this.set("valid", false);
        this.set("invalidMessage", 
                "This selection is not an available option.");
        return next();
    }

    return next();
}


function getSelectedOption(selection, options) {
    var selectedOption = null;
    if (typeof selection === "string") {
        // finds the corresponding value in options
        for (var i = 0; i < options.length && !selectedOption; i++) {
            if (options[i].name === selection) {
                selectedOption = option[i];
            }
        }
    } else {
        if (options.indexOf(selection) !== -1) {
            selectedOption = selection;
        }
    }
    return selectedOption;
}

This gist is untested yet! It is currently an incomplete answer to formix/infernal-engine#39