This principle is akin to staging in theatre, as it is known in theatre and film.[11] Its purpose is to direct the audience's attention, and make it clear what is of greatest importance in a scene;[12] Johnston and Thomas defined it as "the presentation of any idea so that it is completely and unmistakably clear", whether that idea is an action, a personality, an expression, or a mood.[11] This can be done by various means, such as the placement of a character in the frame, the use of light and shadow, or the angle and position of the camera.[13] The essence of this principle is keeping focus on what is relevant, and avoiding unnecessary detail.[14][15]