Mac OS X uses passwords in numerous different settings, each with its own purpose. In the next few pages, I list the most common places you find passwords on a Mac and explain each one's purpose.
Which characters can you include in these passwords? Unless otherwise noted, the following guidelines apply:
For passwords that protect information or services on your Mac itself (your user account, keychain, disk images, and so on), you can use any character you can type on a U.S. English keyboard, including Option+key combinations. However, remember that you normally don't see your password when typing it (you usually see bullet characters or asterisks instead), so don't choose characters you're unable to type correctly without visual feedback.
For passwords processed by other devices — a Wi-Fi access point, a web server, a network file server — you should generally stick with characters visible on a U.S. English keyboard — capital and lowercase letters, numbers, and punctuation are usually acceptable, but any characters typed by using Option+key combinations should be avoided.
As a general rule, it's wise to avoid the space character in a password, which can confuse a computer in certain situations (such as typing instructions on the command line in Terminal). Likewise, single and double quotation marks can sometimes be misconstrued, so it's safest not to use them.
Every user account in Mac OS X has its own password, ...