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+Normally, the content of files in the annex is prevented from being modified.
+That's a good thing, because it might be the only copy, you wouldn't
+want to lose it in a fumblefingered mistake.
+
+	# echo oops > my_cool_big_file
+	bash: my_cool_big_file: Permission denied
+
+In order to modify a file, it should first be unlocked.
+
+	# git annex unlock my_cool_big_file
+	unlock my_cool_big_file (copying...) ok
+
+That replaces the symlink that normally points at its content with a copy
+of the content. You can then modify the file like any regular file. Because
+it is a regular file.
+
+(If you decide you don't need to modify the file after all, or want to discard
+modifications, just use `git annex lock`.)
+
+When you `git commit`, git-annex's pre-commit hook will automatically
+notice that you are committing an unlocked file, and add its new content
+to the annex. The file will be replaced with a symlink to the new content,
+and this symlink is what gets committed to git in the end.
+
+	# echo "now smaller, but even cooler" > my_cool_big_file
+	# git commit my_cool_big_file -m "changed an annexed file"
+	add my_cool_big_file ok
+	[master 64cda67] changed an annexed file
+	 2 files changed, 2 insertions(+), 1 deletions(-)
+	 create mode 100644 .git-annex/WORM:1289672605:30:file.log
+
+There is one problem with using `git commit` like this: Git wants to first
+stage the entire contents of the file in its index. That can be slow for
+big files (sorta why git-annex exists in the first place). So, the
+automatic handling on commit is a nice safety feature, since it prevents
+the file content being accidentally committed into git. But when working with
+big files, it's faster to explicitly add them to the annex yourself
+before committing.
+
+	# echo "now smaller, but even cooler yet" > my_cool_big_file
+	# git annex add my_cool_big_file
+	add my_cool_big_file ok
+	# git commit my_cool_big_file -m "changed an annexed file"