diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a71a37a..a43ac1a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -75,7 +75,7 @@ jobs:
     - uses: actions/checkout@v3
     - run: |
         # Make Bash not silently ignore errors.
-        set -euo pipefail
+        set -euxo pipefail
 
         # Install the appropriate version of Rust.
         rustup toolchain install 1.76.0 # [ref:rust_1.76.0]
diff --git a/README.md b/README.md
index ef2a4be..75164a9 100644
--- a/README.md
+++ b/README.md
@@ -10,17 +10,19 @@ Tagref works with any programming language, and it respects your `.gitignore` fi
 
 ## What is it?
 
-Tagref allows you to annotate your code with *tags* (in comments) which can be *referenced* from other parts of the codebase. For example, you might have a tag like this:
+Tagref allows you to annotate your code with *tags* (in comments) which can be *referenced* from other parts of the codebase. For example, the following function has an important postcondition which is labeled with a tag:
 
 ```python
-# [tag:cities_nonempty] There should be at least one city here.
-cities = ['San Francisco', 'Tokyo']
+# [tag:polynomial_nonzero] This function never returns zero.
+def polynomial(x):
+  return x ** 2 + 1
 ```
 
-Elsewhere, suppose you're writing some code which depends on that fact. You can make that clear by referencing the tag:
+Elsewhere (possibly in a different file), suppose you're writing some code which depends on that fact. You can make that clear by referencing the tag:
 
 ```python
-first_city = cities[0] # This is safe due to [ref:cities_nonempty].
+def inverse_polynomial(x):
+  return 1 / polynomial(x) # This is safe due to [ref:polynomial_nonzero].
 ```
 
 To help you manage these tags and references, Tagref checks the following: