This is the minimum acceptable GML that 000000book will accept. It will reject with 'invalid GML' if it cannot parse or if required tags are missing.

<gml>
<tag>
<drawing>
    <stroke> /* by default stroke drawing is true */
        <pt>
            <x>0.0</x>
            <y>0.0</y>
        </pt>
        <pt>
            <x>0.0</x>
            <y>0.0</y>
        </pt>
        <pt>
            <x>0.0</x>
            <y>0.0</y>
        </pt>    
    </stroke>
</drawing>
</tag>
</gml>