Comics is a medium used to express ideas with images, often combined with text or other visual information. It typically takes the form of a sequence of panels of images. Textual devices such as speech balloons, captions, and onomatopoeia can indicate dialogue, narration, sound effects, or other information. There is no consensus amongst theorists and historians on a definition of comics; some emphasize the combination of images and text, some sequentiality or other image relations, and others historical aspects such as mass reproduction or the use of recurring characters. Cartooning and other forms of illustration are the most common image-making means in comics; fumetti is a form that uses photographic images. Common forms include comic strips, editorial and gag cartoons, and comic books