The Web site visit counter (b) that accumulates the number of different visitors to a Web site is a server-side application, because the count must be updated and maintained on the server. At best, a client-side counter could keep track of the number of visits the user has made to a site and report to the user how many times he or she has been to the site. The storage requires scripting the cookie (see Chapter 16). A chat room application (c) done properly requires server facilities to open up communication channels among all users connected simultaneously. Client-side scripting by itself cannot create a live chat environment.
Valid, because it is one contiguous word. InterCap spelling is fine.
Valid, because an underscore character is acceptable between words.
Not valid, because an identifier cannot begin with a numeral.
Not valid, because no spaces are allowed.
Not valid, because apostrophes and ...