From a4d1f4e99587deaeeae82db2715beda38a33fda7 Mon Sep 17 00:00:00 2001
From: Oscar Gustafsson <oscar.gustafsson@gmail.com>
Date: Tue, 12 Sep 2023 11:06:47 +0200
Subject: [PATCH] Use cbook methods for string checking

---
 lib/matplotlib/_mathtext.py | 2 +-
 lib/matplotlib/legend.py    | 4 ++--
 lib/matplotlib/rcsetup.py   | 4 ++--
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
index b23cb67116ed..0d8842772a5b 100644
--- a/lib/matplotlib/_mathtext.py
+++ b/lib/matplotlib/_mathtext.py
@@ -2766,7 +2766,7 @@ def _auto_sized_delimiter(self, front: str,
             depth = max([x.depth for x in middle if not isinstance(x, str)])
             factor = None
             for idx, el in enumerate(middle):
-                if isinstance(el, str) and el == '\\middle':
+                if el == r'\middle':
                     c = T.cast(str, middle[idx + 1])  # Should be one of p.delims.
                     if c != '.':
                         middle[idx + 1] = AutoHeightChar(
diff --git a/lib/matplotlib/legend.py b/lib/matplotlib/legend.py
index fcd7850bb473..14249cb73442 100644
--- a/lib/matplotlib/legend.py
+++ b/lib/matplotlib/legend.py
@@ -29,7 +29,7 @@
 import numpy as np
 
 import matplotlib as mpl
-from matplotlib import _api, _docstring, colors, offsetbox
+from matplotlib import _api, _docstring, cbook, colors, offsetbox
 from matplotlib.artist import Artist, allow_rasterization
 from matplotlib.cbook import silent_list
 from matplotlib.font_manager import FontProperties
@@ -622,7 +622,7 @@ def __init__(
                         break
                     except AttributeError:
                         pass
-        elif isinstance(labelcolor, str) and labelcolor == 'none':
+        elif cbook._str_equal(labelcolor, 'none'):
             for text in self.texts:
                 text.set_color(labelcolor)
         elif np.iterable(labelcolor):
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
index 276bb9f812a9..c289459b1874 100644
--- a/lib/matplotlib/rcsetup.py
+++ b/lib/matplotlib/rcsetup.py
@@ -179,7 +179,7 @@ def _make_type_validator(cls, *, allow_none=False):
 
     def validator(s):
         if (allow_none and
-                (s is None or isinstance(s, str) and s.lower() == "none")):
+                (s is None or cbook._str_lower_equal(s, "none"))):
             return None
         if cls is str and not isinstance(s, str):
             raise ValueError(f'Could not convert {s!r} to str')
@@ -615,7 +615,7 @@ def _validate_minor_tick_ndivs(n):
     two major ticks.
     """
 
-    if isinstance(n, str) and n.lower() == 'auto':
+    if cbook._str_lower_equal(n, 'auto'):
         return n
     try:
         n = _validate_int_greaterequal0(n)