gh-123858: Improve Doc: SyntaxWarning is emitted during bytecode generation (gh-122844)

---------

Co-authored-by: Alyssa Coghlan <[email protected]>

Author: bebound

Doc/library/exceptions.rst

@@ -897,6 +897,9 @@ The following exceptions are used as warning categories; see the
 
    Base class for warnings about dubious syntax.
 
+   This warning is typically emitted when compiling Python source code, and usually won't be reported
+   when running already compiled code.
+
 
 .. exception:: RuntimeWarning
 

Doc/library/warnings.rst

@@ -80,7 +80,9 @@ The following warnings category classes are currently defined:
 |                                  | unless triggered by code in ``__main__``).    |
 +----------------------------------+-----------------------------------------------+
 | :exc:`SyntaxWarning`             | Base category for warnings about dubious      |
-|                                  | syntactic features.                           |
+|                                  | syntactic features (typically emitted when    |
+|                                  | compiling Python source code, and hence       |
+|                                  | may not be suppressed by runtime filters)     |
 +----------------------------------+-----------------------------------------------+
 | :exc:`RuntimeWarning`            | Base category for warnings about dubious      |
 |                                  | runtime features.                             |