Hi, I'm trying to create an add-on that uses multi-selection check boxes (such as admin.php?options/edit-option/spamDefaultOptions). I've managed to get the output I want by simply editing the sub-array names to be what I want and then using the following in my template; However, I don't really understand what the values in array mean. I have figured out that a:5 is because you have 5 array sub-options and the numbers in quotes (1 or 0) appear to dictate whether the check box should be checked (1) or unchecked (0) by default. It is the rest of the letters/numbers I don't understand, s:1, s:9, etc. What does these values mean? Any help greatly appreciated.