Method names in Ruby may contain upper-case and lower-case letters,
numbers, underscores _ and the punctation signs !, ?, =.
A method name can't begin with a number,
and the characters !, ? and = can only appear at the end.
Non-ASCII characters can be used in a method name,
but this can lead to very confusing situations and should not be common practice.
It's good practice, while not mandatory,
to start the method name with a lower-case character,
because names that start with capital
letters are constants in Ruby.
It's still possible to use a constant name for a method,
but you won't be able to invoke it without parentheses,
because the interpeter will look-up for the name as a constant: