Symbols
=======

   A "symbol" is one or more characters chosen from the set of all
letters (both upper and lower case), digits and the two characters `_.'
On most machines, you can also use `$' in symbol names; exceptions are
noted in See Machine Dependent.  No symbol may begin with a digit.
Case is significant.  There is no length limit: all characters are
significant.  Symbols are delimited by characters not in that set, or
by the beginning of a file (since the source program must end with a
newline, the end of a file is not a possible symbol delimiter).  
See Symbols.