The role of a film editor is to select shots from raw footage and arrange them in an effective sequence to tell the story. An editor must create smooth transitions between shots to convey tone, the passage of time, or separate story parts. Editing is referred to as an "invisible art" because the editor constructs the story in a way that engages viewers without them noticing the editing work. Modern editors use digital software to easily edit, alter, and enhance video clips and audio. Effective editing maintains continuity, elicits emotion, and ensures the viewer understands the story.