<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1 Tiny//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-tiny.dtd">
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">

<!-- an1: Change width from 10 to 50 in 4s -->
<!-- an2: Change width from 10 to 25 + additive=sum. This results in a change from 20 to 75 -->
<!-- an3: Change width from 0 to 25 + additve=sum. This results in a final change from 20 to 100 -->
<rect width="10" height="100" fill="green">
    <animate id="an1" attributeType="XML" attributeName="width" fill="freeze" from="10" to="50" begin="0s" dur="4s"/>
    <animate id="an2" attributeType="XML" attributeName="width" additive="sum" fill="freeze" from="10" to="25" begin="0s" dur="4s"/>
    <animate id="an3" attributeType="XML" attributeName="width" additive="sum" fill="freeze" from="0" to="25" begin="0s" dur="4s"/>
</rect>

</svg>