I've tried to make it so that the class makes no assumptions about the file's contents, and the way it writes the file should be safe from multiple hits to it simultaneously. I can't guarantee that though. The PHP maintainers really need to implement some kind of file locking routines. If you're concerned that this may become a problem, you'll need to implement some kind of locking procedure within your own program. If a method returns an error, or a method fails, the error can be retrived by looking at this variable for the error text.
Turns logging of errors on or off, default is true.
If starting a new password file, will remain false until the first user is added to the file, then will be true from then on out. The version of this class file. The raw file contents as one big scalar. Allows you to perform your own functions upon the raw data. If at any time this class cannot write a file it needs to write, it will immediately exit the entire program, rather than compromise security by assuming the file was successfully written.