diff --git a/README.md b/README.md
index 901d6a4..f888791 100644
--- a/README.md
+++ b/README.md
@@ -2,8 +2,8 @@
 
 This is a brief introduction to python packages. How to make them, how
 to install them, how to upload them, how to maintain them, how to work
-with them. For details consult https://packaging.python.org and other
-sites.
+with them. For details consult https://packaging.python.org, or
+https://py-pkgs.org, or other sites.
 
 
 ## Why packages?
@@ -193,6 +193,22 @@ python3 -m twine upload dist/*
 token
 
 
+## Versioning
+
+Your package needs a version number (for details se below). But how to
+choose the right version number? A nice and brief overview is given at
+the [Python Packaging User
+Guide](https://packaging.python.org/en/latest/discussions/versioning/).
+
+In short, for semantic versioning the version number is composed of
+three integer numbers called `major`, `minor`, and `patch`, separated
+by a dot. These numbers are incremented in the following way:
+
+- `major`, when incompatible API changes have been introduced,
+- `minor`, when functionality is added in a backwards-compatible manner, and
+- `patch`, for backwards-compatible bug fixes.
+
+
 ## Package version
 
 For uploading your package to [PyPi](https://pypi.org/) you need to
@@ -235,14 +251,15 @@ def about():
 
 But how do you get the very same version into the `pyproject.toml`
 file? It would be a very bad idea to write it there directly and
-update it whenever you change it in the `__init__.py` file.
-
-For this you need to specify the `version` field as `dynamic` in the
-`[project]` section. This tells the package tool that the version will
-be set dynamically by some code. There are several options to do
-so. The simplest one is to add a `[tool.setuptools.dynamic]` section
-where the version is read as an attribute from the `numerix` package,
-that is its `__init__.py`file:
+update it whenever you change it in the `__init__.py` file. The
+version number should be set only in one place.
+
+This is possible, of course.  You need to specify the `version` field
+as `dynamic` in the `[project]` section. This tells the package tool
+that the version will be set dynamically by some code. There are
+several options to do so. The simplest one is to add a
+`[tool.setuptools.dynamic]` section where the version is read as an
+attribute from the `numerix` package, that is its `__init__.py`file:
 
 ```txt
 ...