Valid characters: lowercase or uppercase Latin letters, numbers, period. Start of line: all available characters except period; Middle of line: all of the available characters except two or more dots in a row; End of line: all characters available except period; Min length: 5 characters, except dots; Max length: 15 characters;

/^[a-zA-Z0-9]([a-zA-Z0-9\.]{0,13}[a-zA-Z0-9])$/