Text on a Path using tspan

<svg width="900" height="200">
<path id="MyPath" d="M 20 100 
C 100 20 180   -60 260 20
C 340 100 420 180 500 100
C 580 20 660 20 660 20" style="fill:none; stroke:yellow; stroke-width:3" />
<text style="font-family:Verdana; font-size:32; fill:aqua">
      We go       <tspan dy="-30" style="fill:red">
        up      </tspan>
     <tspan dy="30">
        ,     </tspan>
      then we go down, then up again
</textPath>
</text>
</svg>