In this chapter, we use a medium as a destination for output. The medium has a drawing plane, two designs called the medium's foreground and background, a transformation, a clipping region, a line style, and a text style. There are per-medium, dynamically scoped, default drawing options. Different medium classes are provided to allow programmers to draw on different sorts of devices, such as displays, printers, and virtual devices such as bitmaps. [annotate]
Many sheets can be used for doing output, so the drawing functions can also take a sheet as the output argument. In this case, drawing function "trampolines" to the sheet's medium. So, while the functions defined here are specified to be called on sheets, they can also be called on sheets. [annotate]
A stream is a special kind of sheet that implements the stream protocol; streams include additional state such as the current text cursor (which is some point in the drawing plane). [annotate]
By default, the "fundamental" coordinate system of a CLIM stream (not a general sheet or medium, whose fundamental coordinate system is not defined) is a left handed system with x increasing to the right, and y increasing downward. (0,0) is at the upper left corner. [annotate]