PEP 765: specify when the SyntaxWarning will be emitted, and explain …

…why (#4132)

peps/pep-0765.rst

@@ -132,6 +132,16 @@ However, we specify here that a ``SyntaxError`` is permitted by
 the language spec, so that other Python implementations can choose
 to implement that.
 
+The CPython implementation will emit the ``SyntaxWarning`` during
+``AST`` construction, to ensure that the warning will show up during
+static anlaysis and compilation, but not during execution of
+pre-compiled code.  We expect that the warning will be seen by a
+project maintainer (when they run static analysis, or CI which
+does not have precompiled files). However, end users of a project
+will only see a warning if they skip precompilation at installation
+time, check installation time warnings, or run static analysis over
+their dependencies.
+
 Backwards Compatibility
 =======================