diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
index 94c1def6..e39ed9da 100644
--- a/.github/workflows/python-package.yml
+++ b/.github/workflows/python-package.yml
@@ -18,9 +18,9 @@ jobs:
             matrix:
                 os: [ubuntu-22.04]
                 python-version: ['3.10']
-                astropy-version: ['<6.1']
+                astropy-version: ['<6.1']  # Compatilbilty with desiconda 20240425-2.2.0.
                 fitsio-version: ['==1.2.1', '<2']
-                numpy-version: ['<1.23']
+                numpy-version: ['<1.23']  # Compatilbilty with desiconda 20240425-2.2.0.
         env:
             DESIUTIL_VERSION: 3.4.3
             # DESIMODEL: ${GITHUB_WORKSPACE}/desimodel
@@ -73,9 +73,9 @@ jobs:
             matrix:
                 os: [ubuntu-22.04]
                 python-version: ['3.10']
-                astropy-version: ['<6.1']
+                astropy-version: ['<6.1']  # Compatilbilty with desiconda 20240425-2.2.0.
                 fitsio-version: ['<2']
-                numpy-version: ['<1.23']  # to keep asscalar, used by astropy
+                numpy-version: ['<1.23']  # Compatilbilty with desiconda 20240425-2.2.0.
         env:
             DESIUTIL_VERSION: 3.4.3
             # DESIMODEL: ${GITHUB_WORKSPACE}/desimodel
diff --git a/requirements.txt b/requirements.txt
index 27ce4bf5..af24e468 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,13 +1,19 @@
-# numpy<1.20
 pytz
 requests
+# Ensure scipy dependency does not bring in a recent version of numpy.
 scipy<1.9
+# The version of astropy will be reset by GitHub Actions tests.
 astropy
+# Ensure compatibility with numpy <1.23.
 numba<0.60
+# Ensure compatibility with numpy <1.23.
 matplotlib<3.9
 healpy
+# It is becoming difficult to install speclite and specsim directly from
+# git+https, so installing from PyPI is definitely preferred here.
 speclite
 specsim
+# The version of fitsio will be reset by GitHub Actions tests.
 fitsio
 # Install desiutil separately since it is needed for the other installs.
 # git+https://github.com/desihub/desiutil.git@3.1.0#egg=desiutil