It appears that when I mass edited documentation pages titles recently in this commit :
I forgot one rule on the way :
To fix this issue, I intend to publish 2 pull requests very soon.
Update: Makefile - Check for rule ids in docs titles (Fixes #969)
Docs: guard-for-in - added missing id in title (Fixes #969)
Build: Makefile - Check for rule ids in docs titles (Fixes #969)