Comics is a visual medium used to express ideas via images, often combined with text or visual information. Comics frequently takes the form of juxtaposed sequences of panels of images. Often textual devices such as speech balloons, captions, and sound effects ("onomatopoeia") indicate dialogue, narration, or other information. Elements such as size and arrangement of panels control narrative pacing. Cartooning and similar forms of illustration are the most common image-making means in comics; fumetti is a form which uses photographic images. Common forms of comics include comic strips, editorial and gag cartoons, and comic books. Since the late 20th century, bound volumes such as graphic novels, comics albums, and tankōbon have become increasingly common, and online webcomics have proliferated.