RemixIconEx.Editor.underline

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

underline(icon_css_class \\ "icon")

iex> Elixir.RemixIconEx.Editor.underline()
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" class="icon">
  <path d="M8 3v9a4 4 0 1 0 8 0V3h2v9a6 6 0 1 1-12 0V3h2zM4 20h16v2H4v-2z" />
</svg>

example usage

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