These basic presentation types correspond to the Common Lisp types of the same name.
t
Summary: The supertype of all other presentation types.
nil
Summary: The subtype of all other presentation types. This has no printed representation, and is useful only in writing "context independent" translators, that is, translators whose to-type is nil .
null
Summary: The presentation type that represents "nothing." The single object associated with this type is nil , and its printed representation is "None."
boolean
Summary: The presentation type that represents t or nil . The textual representation is "Yes" and "No," respectively.
symbol
Summary: The presentation type that represents a symbol.
keyword
Summary: The presentation type that represents a symbol in the keyword package. It is a subtype of symbol .
blank-area
Summary: The type that represents all the places in a window where there is no presentation that is applicable in the current input context. CLIM provides a single "null presentation" as the object associated with this type.
*null-presentation*
Summary: The null presentation, which occupies all parts of a window in which there are no applicable presentations. This will have a presentation type of blank-area .
Common Lisp Interface Manager 2.0 User's Guide - 20 Sep 2011