diff --git a/Doc/library/warnings.rst b/Doc/library/warnings.rst
index f7a1f70833b..43708f8021a 100644
--- a/Doc/library/warnings.rst
+++ b/Doc/library/warnings.rst
@@ -154,14 +154,19 @@ the disposition of the match.  Each entry is a tuple of the form (*action*,
   +---------------+----------------------------------------------+
 
 * *message* is a string containing a regular expression that the start of
-  the warning message must match.  The expression is compiled to always be
-  case-insensitive.
+  the warning message must match, case-insensitively.  In :option:`-W` and
+  :envvar:`PYTHONWARNINGS`, *message* is a literal string that the start of the
+  warning message must contain (case-insensitively), ignoring any whitespace at
+  the start or end of *message*.
 
 * *category* is a class (a subclass of :exc:`Warning`) of which the warning
   category must be a subclass in order to match.
 
-* *module* is a string containing a regular expression that the module name must
-  match.  The expression is compiled to be case-sensitive.
+* *module* is a string containing a regular expression that the start of the
+  fully-qualified module name must match, case-sensitively.  In :option:`-W` and
+  :envvar:`PYTHONWARNINGS`, *module* is a literal string that the
+  fully-qualified module name must be equal to (case-sensitively), ignoring any
+  whitespace at the start or end of *module*.
 
 * *lineno* is an integer that the line number where the warning occurred must
   match, or ``0`` to match all line numbers.
@@ -207,8 +212,7 @@ Some examples::
    error::ResourceWarning       # Treat ResourceWarning messages as errors
    default::DeprecationWarning  # Show DeprecationWarning messages
    ignore,default:::mymodule    # Only report warnings triggered by "mymodule"
-   error:::mymodule[.*]         # Convert warnings to errors in "mymodule"
-                                # and any subpackages of "mymodule"
+   error:::mymodule             # Convert warnings to errors in "mymodule"
 
 
 .. _default-warning-filter:
diff --git a/Misc/NEWS.d/next/Documentation/2022-05-26-11-33-23.gh-issue-86438.kEGGmK.rst b/Misc/NEWS.d/next/Documentation/2022-05-26-11-33-23.gh-issue-86438.kEGGmK.rst
new file mode 100644
index 00000000000..75abfdd63b8
--- /dev/null
+++ b/Misc/NEWS.d/next/Documentation/2022-05-26-11-33-23.gh-issue-86438.kEGGmK.rst
@@ -0,0 +1,3 @@
+Clarify that :option:`-W` and :envvar:`PYTHONWARNINGS` are matched literally
+and case-insensitively, rather than as regular expressions, in
+:mod:`warnings`.