Answer 1

<svg width="800" height="800">
<polyline style="stroke-linejoin:miter; stroke:yellowgreen;stroke-width:9; fill: none;"
points="100 100,200 0"/>
</svg>

"100 100,200 0" has a format of "x y,x1 y1"
Imagination~
First point at x:100 y:100 of svg
Second point at x:200 y:0 of svg

I ever confused with that too -_-
Because I see it into "n x,y n"