First thing. For those who use vim but might not have known about it: vim has a feature called digraphs which gives you a way to enter letters with diacritics (eg ä), symbols (eg ✓), and other characters that aren't on your keyboard. It does have its idiosyncracies, but it's fairly reasonable once you start to toy with it a bit.
How it works: first, enter the compose key, which by default is Control-K. Then enter the two characters of the digraph, and you'll get the single character that's defined in the digraphs table for that particular combination.
So, for instance:
- Ctrl-K + o + - ⇒ ō
- Ctrl-K + e + : ⇒ ë
- Ctrl-K + c + , ⇒ ç
- Ctrl-K + o + C ⇒ ℃
- Ctrl-K + P + d ⇒ £
- Ctrl-K + 1 + 2 ⇒ ½
The command :digraphs will show you everything in the digraphs table.
Last thing and the point of all that preparatory context above: there is a terrible problem with the set of digraphs as it ships with vim. Clearly the sequence < + 3 should compose to the character ♥, but it doesn't by default. To remedy this horrible shortcoming, add the line
digraph <3 9829
to your vim config file. (9829 is the unicode decimal identifier for the character ♥.)