Apple II character set
The Apple II character set was based on ASCII, but as with other small computers of the day, it had a few platform-specific quirks.
It was a 7-bit character set, with the 8th bit used for other purposes in input and output such as denoting inverse video or keyboard buffering.
In the original Apple II models, only uppercase letters were used, with the lowercase letters displaying as punctuation from elsewhere in ASCII. Later models (starting with the IIe) had lowercase support (and there were third-party addons to add this capability to older Apples).
Early Apples had left and right arrows, with up and down arrows being added in later models. These keys mapped onto characters in the C0 controls range: BS (09) for left, NAK (15) for right, VT (0B) for up, and LF (0A) for down. Other control characters used in the Apple included CR (0D) used as a newline and ENTER character, BEL (07) which sounded the Apple speaker (the "G" key was marked "BELL" in the earliest Apples to suggest this use for Ctrl-G), and EOT / Ctrl-D (04) which signified that what followed was a DOS command. Also, Ctrl-Y / EM (19) was used in the assembly-language monitor (which the earliest Apples started up in; it was much less frequently encountered later on) to run a user-specified callback routine.
Since text displays on early Apples had 40 characters, any text files formatted for them would likely have line breaks before that point. Some programs used high-res graphics to display text characters in place of the standard Apple text mode, so they might have lowercase letters, different line widths, and special characters not in the standard character set.