<svgversion="1.1"xmlns="http://www.w3.org/2000/svg"width="520"height="320"style="background: #eee;"><pathd="
M 20 150
Q 100 50 180 150
T 400 150
T 500 150
"stroke="black"stroke-width="3"fill="none"/></svg>
arbitrary form with Z
<svgversion="1.1"xmlns="http://www.w3.org/2000/svg"width="600"height="320"style="background: #eee;"><pathd="
M 150 150
Q 150 50 250 50
T 350 150
T 250 250
Z
"stroke="#f88"stroke-width="3"fill="#fcc"/></svg>
arbitrary form for domain & boundary
<svgversion="1.1"xmlns="http://www.w3.org/2000/svg"width="600"height="320"style="background: #eee;"><pathd="
M 150 150
Q 150 50 250 50
T 400 150
T 300 250
T 150 150
"stroke="#f88"stroke-width="3"fill="#fcc"/></svg>