2.1.7 [CSS-Level2-2009] Section 4.3.1, Integers and real numbers
Some value types may have integer values (denoted by <integer>) or real number values (denoted by <number>). Real numbers and integers are specified in decimal notation only. An <integer> consists of one or more digits "0" to "9". A <number> can either be an <integer>, or it can be zero or more digits followed by a dot (.) followed by one or more digits. Both integers and real numbers may be preceded by a "-" or "+" to indicate the sign. -0 is equivalent to 0 and is not a negative number.
Quirks Mode (All Versions)
A <number> that has no digits following the dot (.) is allowed. For example, "10.em" is correctly parsed.