TL;DR: it does this by generating shell aliases which use $EDITOR to open the file. Neat, but does it clean up the aliases when you use one? And what if you don't use any? Kinda makes my OCD cringe a bit.
[alias]
grepgvim = "!f() { git grep -l \"$@\" | xargs gvim -p; }; f"
To the Tag author, maybe users would find this tidier if `tag` let you edit matches directly by invoking e.g. `tag func -e 96` and tag will do the rest?
In such a scheme someone could even set the alias file to `/dev/null` and it'd allow both the current workflow and a new one that didn't rely on aliases.
EDITOR="FOO"
$EDITOR $FILE
~/badcode$ echo "func" > badfile.go\;\ echo\ \"Gotcha\!\"
~/badcode$ ls
badfile.go; echo "Gotcha!"
~/badcode$ tag func
badfile.go; echo "Gotcha!"
[1] 1:func
~/badcode$ e1
Gotcha! +1
Other ways to implement the shortcuts: create a flag or subcommand to look up an hit from the results file and jump to it (I can alias this command to suit my taste) or prompt me for input before returning to the command line.