Separator is a horizontal or a vertical line. The following panel has a button('Left'), a vertical separator line, and a second button ('Right') in the first row, a horizontal separator in the second row, and the final button ('Bottom') in the third row.

<panel columns="3" gap="4" top="4" left="4">
  <button text="Left" />
  <separator />
  <button text="Right" />
  <separator colspan="3" />
  <button text="Bottom" colspan="3" />

name, enabled, visible, tooltip, property, width, height, colspan, rowspan, weightx, weighty, halign, and valign parameters are similar to component