Nucleus has some built-in rules concerning comments:

• words longer than 90 characters are not allowed (why: layout might get messed up when people do that)
• the actual comment should be at least 3 characters long
• comments cannot be longer than 5000 characters
• guests need to enter a username of at least 2 characters
• guests cannot use quotes or newlines in username/email
• each sequence of 3 newlines in the body gets replaced by a single newline (why: layout)
• HTML tags are replaced by entities
• the comment is trimmed (leading and trailing whitespace is left of)
• URLs are 'hreffed'. To avoid layout mess-ups, the URLs are shortened.

As for now, all of these rules and parameters are hardwired into the code.