A constant symbol starts with a digit (0-9) or a period.
You cannot change the value of a constant symbol. It is simply the string consisting of the characters of the symbol (that is, with any lowercase alphabetic characters translated to uppercase).
These are constant symbols:
Example 1.21. Constants
77
827.53
.12345
12e5 /* Same as 12E5 */
3D
17E-3
Symbols, where the first character is a period and the second character is alphabetic, are environment symbols (Section 1.13.6, “Environment Symbols”) and may have a value other other than the symbol name.
