Issue #23921: Standardized documentation whitespace formatting.

Original patch by James Edwards.

Doc/library/html.parser.rst

@@ -51,8 +51,10 @@ as they are encountered::
    class MyHTMLParser(HTMLParser):
        def handle_starttag(self, tag, attrs):
            print("Encountered a start tag:", tag)
+
        def handle_endtag(self, tag):
            print("Encountered an end tag :", tag)
+
        def handle_data(self, data):
            print("Encountered some data  :", data)
 
@@ -237,21 +239,27 @@ examples::
            print("Start tag:", tag)
            for attr in attrs:
                print("     attr:", attr)
+
        def handle_endtag(self, tag):
            print("End tag  :", tag)
+
        def handle_data(self, data):
            print("Data     :", data)
+
        def handle_comment(self, data):
            print("Comment  :", data)
+
        def handle_entityref(self, name):
            c = chr(name2codepoint[name])
            print("Named ent:", c)
+
        def handle_charref(self, name):
            if name.startswith('x'):
                c = chr(int(name[1:], 16))
            else:
                c = chr(int(name))
            print("Num ent  :", c)
+
        def handle_decl(self, data):
            print("Decl     :", data)
 
@@ -283,7 +291,7 @@ further parsing::
         attr: ('type', 'text/css')
    Data     : #python { color: green }
    End tag  : style
-   >>>
+
    >>> parser.feed('<script type="text/javascript">'
    ...             'alert("<strong>hello!</strong>");</script>')
    Start tag: script