I ran :help index
to find out about key mappings and it's great, but there's one thing I don't get. At the top it says...
This file contains a list of all commands for each mode, with a tag and a short description.
Indeed, the leftmost column of information in each section is "tag".
So e.g., the first thing is...
tag char action in Insert mode
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i_CTRL-@ CTRL-@ insert previously inserted text and stop
What is the nature and purpose of the tag i_CTRL-@
?
Does it do something useful I should know about?