pathLength

html,
body,
svg {
  height: 100%;
}

<svg viewBox="0 0 100 60" xmlns="http://www.w3.org/2000/svg">
  <style>
    path {
      fill: none;
      stroke: black;
      stroke-width: 2;
      stroke-dasharray: 10;
    }
  </style>

  <!-- No pathLength, the real length of the path is used. In that case, 100 user units -->
  <path d="M 0,10 h100" />

  <!-- compute everything like if the path length was 90 user units long -->
  <path d="M 0,20 h100" pathLength="90" />

  <!-- compute everything like if the path length was 50 user units long -->
  <path d="M 0,30 h100" pathLength="50" />

  <!-- compute everything like if the path length was 30 user units long -->
  <path d="M 0,40 h100" pathLength="30" />

  <!-- compute everything like if the path length was 10 user units long -->
  <path d="M 0,50 h100" pathLength="10" />
</svg>