The following characters are permitted when specifying Class names and Module names:  Contains lowercase characters, numbers, and underscores.  Scope Resolution Operators, i.e. "::" are namespace separators in class name definition.  The acceptable characters for Variable names are listed below:  Can start with both capital and small letters.  Numerals and underscores ('_') are permitted.  If the variable's initial character is an underscore, it is only available inside its own local scope.