[3.12] gh-107607: Update comment about utf-8 BOM being ignored (GH-107858) (#117016)

(cherry picked from commit 7f64ae3)
Co-authored-by: Terry Jan Reedy [email protected]

Author: miss-islington

Doc/reference/lexical_analysis.rst

@@ -96,10 +96,9 @@ which is recognized also by GNU Emacs, and ::
 
 which is recognized by Bram Moolenaar's VIM.
 
-If no encoding declaration is found, the default encoding is UTF-8.  In
-addition, if the first bytes of the file are the UTF-8 byte-order mark
-(``b'\xef\xbb\xbf'``), the declared file encoding is UTF-8 (this is supported,
-among others, by Microsoft's :program:`notepad`).
+If no encoding declaration is found, the default encoding is UTF-8.  If the
+implicit or explicit encoding of a file is UTF-8, an initial UTF-8 byte-order
+mark (b'\xef\xbb\xbf') is ignored rather than being a syntax error.
 
 If an encoding is declared, the encoding name must be recognized by Python
 (see :ref:`standard-encodings`). The