We can use (check-parens) to find an unmatched parenthesis or string quote.

We can use (Info-index), default keybinding i, when inside an Emacs manual page to search the index for topics.

We can use git grep to search through the commit history of tracked files:

git rev-list --all | xargs git grep "search terms"

git rev-list –all prints all the commits in reverse chronological order.