Explicitly state limits to characters, number of entries, and so forth
Too many sites give speeding tickets without ever posting speed limit signs. If there is only a narrow range of acceptable characters or entries (for example, a text box with a limit of 20 characters or a field that allows a maximum of 10 emails), make sure you clearly explain the limit. Frustration is sure to ensue if you're not upfront about the limits visitors need to conform to in order to succeed.
Then How Many? mail.yahoo.com
Yahoo! Mail won't send my message because the "Bcc field contains too many addressees." Unfortunately, Yahoo! doesn't tell me how many addressees I can submit. I have to guess and guess again to get the right number. It's a frustrating process that takes too much time to figure out. Obstacles such as this make me want to find a new group mailing list provider.
Why is this bad? It's as if I try to buy 20 tickets to a sporting event but the ticket office refuses me because there is a limit on the number of tickets an individual can buy. The really frustrating part is that the ticket office won't tell me the actual limit! Instead, I have to keep guessing until I hit a number below the maximum.
A similar process occurs when a site requires a limit to the number of characters in a form field. Customers carefully word their entries, so it's essential that you communicate, at the point of entry, the allowable amount of text.
What's the Limit? http://www.cdnow.com
CDNow tells me my "Address Exceeds Maximum Allowable Length" but doesn't tell me the actual maximum length I can use. As a result, I'm left with the tedious trial-and-error method as the only way to determine how much text is allowed. Plus, who uses language such as "exceeds maximum allowable length?"
From the customer...
"Another painful example of this is HotJobs.com. They have a limit on the amount of characters your resumé can contain. (They have a resumé builder tool.) This is annoying for various reasons: 1) I don't want to shorten my resumé. 2) They don't tell me how far over the limit I am when posting. I had to go through about 10 iterations before getting it right. Annoying!"
Your visitors need to know about these sorts of restrictions before they waste time crafting unacceptable entries. Be forthright about any limits and place this information at the point of data entry.
It's also a good idea to offer a countdown feature and use the "Maxlength" attribute (more to follow on this) to cap the number of characters that can be entered in the field. If customers do enter too much text, make sure you clearly explain the problem and how to fix it.
25 Max http://www.google.com
Google helpfully informs me of the maximum number of characters I can enter. The site also uses the Maxlength attribute, so I'm unable to enter more than 25 characters.
Use the Maxlength HTML attribute to specify the maximum number of characters a text entry box can accept. This ensures that a customer won't be able to enter too many characters. Here's an example for how to limit entries (to 50 characters in this case):
<input type="text" name="fieldname" maxlength="50">