Why is animate tag removed from SVG in XML dashboard?

[accpnt]

I have an error while trying to animate an embedded SVG in one of my XML dashboard. I noticed that the animate tag included in a <line> or <rect> root tags is systematically removed from my XML when rendered in the dashboard's HTML (the output). That problem gives me error while trying to parse the <animate> tag with a custom JavaScript, as they are missing from the DOM. 

<line id="id_1" stroke="rgb(0,220,228)" stroke-width="3" visibility="visible" x1="404.0" x2="833.0" y1="1255.0" y2="1255.0">
    <title>id_1</title>
    <desc>description of id_1</desc>
    <metadata>
        <route/>
    </metadata>
    <animate attributeName="stroke" attributeType="CSS" dur="1s" from="rgb(0,220,228)" id="id_1" repeatCount="indefinite" to="white"/>
</line>

I enclosed with this post a sample of the SVG embedded in my dashboard. While rendered as HTML, it looks like this:

<line id="id_1" stroke="rgb(0,220,228)" stroke-width="3" visibility="visible" x1="404.0" x2="833.0" y1="1255.0" y2="1255.0">
    <title>id_1</title>
    <desc>description of id_1</desc>
    <metadata>

    </metadata>

</line>

It used to work on a Splunk 7, but somehow it doesn't work on Splunk 8 and 9. I wanted to know what might cause this error ? And also, can someone provide me docs on how the Splunk XML dashboard are exported as HTML in order to understand which component might explain this problem ?

Are there SVG/XML standards that evolved from Splunk 7 to Splunk 8/9 ?