HTML and CSS Reference
A number value is expressed as a positive or negative number (when permitted). Numbers can
be either real (represented as <number> ) or integers ( <integer> ). They may also restrict the
range of acceptable values, as with color values that accept only integers in the range 0-255.
A more common range restriction is to limit a number to be non-negative. These are some-
times represented as <non-negative number> or <non-negative integer> .