Is there a well documented or well understood explanation for what was the intended purpose for the more haphazard glyph choices in the control code range of the original IBM PC character set? Maybe a design document? It would also be great to understand how the extended character set glyphs were chosen, but that's less important as those (mostly) have an obvious meaning.
The control code (< 32) range in the original IBM PC character set (what we today call codepage 437) is home to an odd mixture of displayable characters. Formally these characters are not displayable in ASCII, but if you put them in the screen buffer most of them display a special character of some sort. It's easy to imagine why you would want to take advantage of otherwise unused character codes for useful characters that they couldn't fit in the extended character (> 127) range.
Many of them have obvious purposes. For example:
- 0x01, 0x02: Smiley faces
- 0x03 - 0x06: Card suits, useful for text-based card games
- 0x18 - 0x1B: Arrows
- 0x14, 0x15: Paragraph marker (Pilcrow) and Section marker, seen in certain types of documents.
However some of them seem (to me) to have been strange choices. For example 0x13 is a double exclamation point which is not something you would normally see in text. 0x17 is a vertical double-arrow with some kind of baseline. There are also an assortment of "bullets" and "reverse bullets" for lack of a better description.
I have to assume someone had a good reason to pick those glyphs specifically. One hypothesis I have is that some of the obscure symbols might have been commonly used by terminal for their status lines (so, useful for terminal emulation), but I don't really have experience with terminals and that's just speculation on my part. Or maybe they are present in older IBM computer equipment and they copied them forward to the IBM-PC? (but that just shifts the question to "what use did that older equipment have for these characters?")
Note that I'm not asking about what common uses were given to those symbols given that they were available, but what was the intended purpose for which they were included in the first place.
(For bonus, 0xFE "black square" is in the extended character range but also doesn't seem to have an obvious purpose to me)