User name form validation message

Question

I have a form validation message for the user name field which says the following

Name can only contain alphabets, '.' and ' ' characters

OR should it be

Name can only contain alphabets, dot and space characters

OR should it be

Name can only contain alphabets, dot (".") and space (" ") characters

Which is preferable from a usability perspective assuming the end users has very less exposure to computers.

Answer 1

• Use 'letters of the alphabet' not 'alphabets'
• rather than 'characters' ''.'' or ("."), why not just show the character on for instance a different background

So something like:

Name can only contain letters of the alphabet, . and spaces

Answer 2

A suggestion: include examples.

Name can only contain letters, dots or spaces. 
E.g. <i>Yoda</i>, <i>Han.Solo</i> or <i>Darth Vader</i> ...