Autocomplete alternative

[stefnotch]

When a symbol perfectly matches, then a new input tree gets created where the autocomplete has been applied. Depending on what the user does next, this new input tree actually gets used, or gets thrown away.

e.g.

• user selects different autocomplete option => throw away
• user hits escape => throw away
• user hits backspace => throw away (?)
• user moves caret => use it
• user types something more => use it

[stefnotch]

Not doing this for now