RemixIconEx.System.filter

You're seeing just the function filter, go back to RemixIconEx.System module for more information.
Link to this function

filter(icon_css_class \\ "icon")

iex> Elixir.RemixIconEx.System.filter()
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" class="icon">
  <path d="M21 4v2h-1l-5 7.5V22H9v-8.5L4 6H3V4h18zM6.404 6L11 12.894V20h2v-7.106L17.596 6H6.404z" />
</svg>

example usage

svg.icon {
  width: 96;
  height: 96;
}