From 67af0f573416a30a2f7e6495020371b11c37007a Mon Sep 17 00:00:00 2001
From: Dan Helfman <witten@torsion.org>
Date: Fri, 22 Dec 2023 21:39:44 -0800
Subject: [PATCH] Document limitation with constant interpolation at the start
 of a value (#741).

---
 docs/how-to/make-per-application-backups.md | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/docs/how-to/make-per-application-backups.md b/docs/how-to/make-per-application-backups.md
index 97ee754a..85951432 100644
--- a/docs/how-to/make-per-application-backups.md
+++ b/docs/how-to/make-per-application-backups.md
@@ -578,6 +578,21 @@ source_directories:
 archive_name_format: 'bar-{now}'
 ```
 
+Note that if you'd like to interpolate a constant into the beginning of a
+value, you'll need to quote it. For instance, this won't work:
+
+```yaml
+source_directories:
+    - {my_home_directory}/.config   # This will error!
+```
+
+Instead, do this:
+
+```yaml
+source_directories:
+    - "{my_home_directory}/.config"
+```
+
 <span class="minilink minilink-addedin">New in version 1.8.5</span> Constants
 work across includes, meaning you can define a constant and then include a
 separate configuration file that uses that constant.