A filename can have up to 255 characters, including spaces.
However, these characters are not allowed in file names:

\            slash

?           question mark

:           colon

*           asterisk

"           quote

<           less than

>           greater than

|            vertical bar

You can use upper and lowercase letters to make your filenames easier to read,
but file names are not case sensitive, thus if you have a file named History 101
and you try to save a file named HISTORY 101, the program will ask you if you want
to overwrite the original file.