Starlight is the quiet end of the glow family. The word rises gently into a night sky and holds there with a slow shimmer while stars twinkle behind it — celestial rather than electrical.
sl-in handles a soft rise, sl-shimmer runs a long, low-amplitude cycle over a feGaussianBlur/feMerge glow. The shimmer period is deliberately slow — fast movement would break the stillness the style depends on.
Yes — it is drawn in the same SVG, so a downloaded file is self-contained and animates on its own with nothing else to load.