Build of the manual now uses venv instead of virtualenv which is bundled with python 3

macOS now includes python3

doc/README

@@ -40,8 +40,9 @@ environment and local folders.
 Installing prerequisites for the documentation build
 
 To run the HTML documention build toolchain, python 3.x, doxygen, git,
-and virtualenv have to be installed.  Also internet access is initially
-required to download external files and tools.
+and the venv python module have to be installed if not already available.
+Also internet access is initially required to download external files
+and tools.
 
 Building the PDF format manual requires in addition a compatible LaTeX
 installation with support for PDFLaTeX and several add-on LaTeX packages

doc/documentation_conventions.md

@@ -22,7 +22,7 @@ conversion from the source to the final formats (HTML, PDF, and
 optionally e-book reader formats ePUB and MOBI) is mostly automated and
 controlled by a Makefile in the `doc` folder. This makefile assumes that
 the processing is done on a Unix-like machine and Python 3.5 or later
-and a matching virtualenv module are available.  Additional Python
+and a matching venv module are available.  Additional Python
 packages (like the Sphinx tool and several extensions) are transparently
 installed into a virtual environment over the internet using the `pip`
 package manager.  Further requirements and details are discussed in the

doc/src/Build_manual.rst

@@ -125,38 +125,29 @@ common setups:
 
       .. code-block:: bash
 
-         sudo apt-get install python-virtualenv git doxygen
+         sudo apt-get install git doxygen
 
    .. tab:: RHEL or CentOS (Version 7.x)
 
       .. code-block:: bash
 
-         sudo yum install python3-virtualenv git doxygen
+         sudo yum install git doxygen
 
    .. tab:: Fedora or RHEL/CentOS (8.x or later)
 
       .. code-block:: bash
 
-         sudo dnf install python3-virtualenv git doxygen
+         sudo dnf install git doxygen
 
-   .. tab:: MacOS X
+   .. tab:: macOS
 
       *Python 3*
 
-      Download the latest Python 3 MacOS X package from
+      If Python 3 is not available on your macOS system, you can
+      download the latest Python 3 macOS package from
       `https://www.python.org <https://www.python.org>`_ and install it.
       This will install both Python 3 and pip3.
 
-      *virtualenv*
-
-      Once Python 3 is installed, open a Terminal and type
-
-      .. code-block:: bash
-
-         pip3 install virtualenv
-
-      This will install virtualenv from the Python Package Index.
-
 Prerequisites for PDF
 ---------------------