Constructs a number snip from its input.
For a number 
num, returns a 
number snip or a
 string according to the specified format arguments.
The exact-prefix argument specifies whether the representation
should carry a #e prefix: Always, never, or when necessary to
identify a representation that would otherwise be considered inexact.
Similarly for inexact-prefix.  Note however that 'when-necessary
is usually equivalent to 'never, as inexact numbers are always
printed with a decimal dot, which is sufficient to identify a number
representation as inexact.
The fraction-view field specifies how exact non-integer reals
- fractions - should be rendered: As a mixed fraction, an improper fraction,
or a decimal, possibly identifying periodic digits.  For 'decimal,
if it’s not possible to render the number as a decimal exactly, a fraction
representation might be generated.  This is currently the case for complex
numbers.
If fraction-view is #f, this option comes from
the 'framework:fraction-snip-style preference.
Makes a 
number snip that shows the decimal expansion for 
number.
The boolean indicates if a 
#e prefix appears on the number.
Makes a 
number snip that shows a fractional view of 
number.
The boolean indicates if a 
#e prefix appears on the number, when
shown in the decimal state.
All values that answer 
#t to this predicate are also 
snip%s.
Overrides the 
on-insert and
after-insert to replace 
number-snip%
objects that look like ASCII with their corresponding ASCII
text.