ANSI Common Lisp 13 Characters 13.1 Character Concepts 13.1.4 Character Categories
18.104.22.168 Graphic Characters
Characters that are classified as graphic, or displayable, are each
associated with a glyph, a visual representation of the character.
A graphic character is one that has a standard textual
representation as a single glyph, such as A or * or =.
Space, which effectively has a blank glyph, is defined
to be a graphic.
Of the standard characters,
newline is non-graphic
and all others are graphic; see Section 2.1.3 Standard Characters.
Characters that are not graphic are called non-graphic.
Non-graphic characters are sometimes informally called
or "control characters."
if they are supported by the implementation,