Doc Update Resolving Issue pallets#2206

- Update CONTRIBUTING.rst with latest Click version
- Add entry_points specification URL
- Clarify shell completion description

CONTRIBUTING.rst

@@ -144,7 +144,7 @@ Start coding
     .. code-block:: text
 
         $ git fetch origin
-        $ git checkout -b your-branch-name origin/8.0.x
+        $ git checkout -b your-branch-name origin/8.1.x
 
     If you're submitting a feature addition or change, branch off of the
     "main" branch.

docs/setuptools.rst

@@ -81,10 +81,12 @@ Contents of ``setup.py``:
         },
     )
 
-The magic is in the ``entry_points`` parameter.  Below
-``console_scripts``, each line identifies one console script.  The first
-part before the equals sign (``=``) is the name of the script that should
-be generated, the second part is the import path followed by a colon
+The magic is in the ``entry_points`` parameter.  Read the full
+`entry_points <https://packaging.python.org/en/latest/specifications/entry-points/>`_
+specification for more details.  Below ``console_scripts``, each
+line identifies one console script.  The first part before the
+equals sign (``=``) is the name of the script that should be
+generated, the second part is the import path followed by a colon
 (``:``) with the Click command.
 
 That's it.

docs/shell-completion.rst

@@ -28,12 +28,16 @@ through an entry point, not through the ``python`` command. See
 :doc:`/setuptools`. Once the executable is installed, calling it with
 a special environment variable will put Click in completion mode.
 
-In order for completion to be used, the user needs to register a special
-function with their shell. The script is different for every shell, and
-Click will output it when called with ``_{PROG_NAME}_COMPLETE`` set to
-``{shell}_source``. ``{PROG_NAME}`` is the executable name in uppercase
-with dashes replaced by underscores. The built-in shells are ``bash``,
-``zsh``, and ``fish``.
+To enable shell completion, the user needs to register a special
+function with their shell. The exact script varies depending on the
+shell you are using. Click will output it when called with
+``_{FOO_BAR}_COMPLETE`` set to ``{shell}_source``. ``{FOO_BAR}`` is
+the executable name in uppercase with dashes replaced by underscores.
+It is conventional but not strictly required for environment variable
+names to be in upper case. This convention helps distinguish environment
+variables from regular shell variables and commands, making scripts
+and configuration files more readable and easier to maintain. The
+built-in shells are ``bash``, ``zsh``, and ``fish``.
 
 Provide your users with the following instructions customized to your
 program name. This uses ``foo-bar`` as an example.
@@ -194,7 +198,7 @@ require implementing some smaller parts.
 
 First, you'll need to figure out how your shell's completion system
 works and write a script to integrate it with Click. It must invoke your
-program with the environment variable ``_{PROG_NAME}_COMPLETE`` set to
+program with the environment variable ``_{FOO_BAR}_COMPLETE`` set to
 ``{shell}_complete`` and pass the complete args and incomplete value.
 How it passes those values, and the format of the completion response
 from Click is up to you.
@@ -207,7 +211,7 @@ formatting with the following variables:
     in the script.
 -   ``complete_var`` - The environment variable name for passing the
     ``{shell}_complete`` instruction.
--   ``prog_name`` - The name of the executable being completed.
+-   ``foo_bar`` - The name of the executable being completed.
 
 The example code is for a made up shell "My Shell" or "mysh" for short.
 
@@ -218,10 +222,10 @@ The example code is for a made up shell "My Shell" or "mysh" for short.
 
     _mysh_source = """\
     %(complete_func)s {
-        response=$(%(complete_var)s=mysh_complete %(prog_name)s)
+        response=$(%(complete_var)s=mysh_complete %(foo_bar)s)
         # parse response and set completions somehow
     }
-    call-on-complete %(prog_name)s %(complete_func)s
+    call-on-complete %(foo_bar)s %(complete_func)s
     """
 
     @add_completion_class