@item (slice @var{x} @var{y} @var{width} @var{height})
This specification together with @code{image} specifies a @dfn{slice}
-(a partial area) of the image to display. The elements @var{y} and
-@var{x} specify the top left corner of the slice, within the image;
-@var{width} and @var{height} specify the width and height of the
-slice. Integers are numbers of pixels. A floating-point number
-in the range 0.0--1.0 stands for that fraction of the width or height
-of the entire image.
+(a partial area) of the image to display. More precisely, the
+specification should have the following form:
+
+@lisp
+ ((slice @var{x} @var{y} @var{width} @var{height}) @var{image-desc})
+@end lisp
+
+@noindent
+where @var{image-desc} is an image descriptor described above. The
+elements @var{x} and @var{y} specify the top left corner of the slice,
+within the image; @var{width} and @var{height} specify the width and
+height of the slice. Integers are numbers of pixels. A floating-point
+number in the range 0.0--1.0 stands for that fraction of the width or
+height of the entire image.
@item ((margin nil) @var{string})
A display specification of this form means to display @var{string}