public void setInstanced(boolean instanced) {
        if (instanced && instanceSpan == 0) {
            instanceSpan = 1;
        } else if (!instanced) {
            instanceSpan = 0;
        }
    }
Sets the instanceSpan to 1 or 0 depending on
the value of instanced and the existing value of
instanceSpan.

@param instanced true for instanced, false for not instanced
jme3-core/src/main/java/com/jme3/scene/VertexBuffer.java