As per the wiki article someone else listed — the compose key was available on keyboards back in the 1980s (notably it was invented only 5 years after the Space Cadet keyboard was invented!).
Some DOS applications did have support for it. The reason it wasn't included is baffling, and it's especially baffling to me that other operating systems never adopted it, simply because
compose a '
is VASTLY more user friendly to type than:
alt-+
1F600
which I have met some windows users who memorize that combo for things like the copyright symbol (which is simply:)
The compose key feels mandatory for anyone who wants to type their native langauge on an US-english layout. The combination[0] is "Compose--." though: –
As it should be. I wish this convention were present across more software, “-“ “- -“ and “- - -“ should be the UI norm for entering proper dashes in text input controls.
compose - -
and it makes an em dash, it takes a quarter of a second longer to produce this.
I don't know why the compose key isn't used more often.