findWireWithInitialStateAreaContaining(pt) {
        // Is it in the right vertical band; the one at the start of the circuit?
        if (pt.x < 0 || pt.x > 30) {
            return undefined;
        }

        // Which wire is it? Is it one that's actually in the circuit?
        let wire = this.wireIndexAt(pt.y);
        if (wire < 0 || wire >= this.circuitDefinition.numWires) {
            return undefined;
        }

        // Is it inside the intended click area, instead of just off to the side?
        let r = this._wireInitialStateClickableRect(wire);
        if (!r.containsPoint(pt)) {
            return undefined;
        }

        // Good to go.
        return wire;
    }
@param {!Point} pt
@returns {undefined|!int}