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diff --git a/lib/unicase/ignorable.c b/lib/unicase/ignorable.c
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+++ b/lib/unicase/ignorable.c
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+/* Test whether a Unicode character is case-ignorable.
+   Copyright (C) 2002, 2006-2007, 2009-2022 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2009.
+
+   This file is free software.
+   It is dual-licensed under "the GNU LGPLv3+ or the GNU GPLv2+".
+   You can redistribute it and/or modify it under either
+     - the terms of the GNU Lesser General Public License as published
+       by the Free Software Foundation, either version 3, or (at your
+       option) any later version, or
+     - the terms of the GNU General Public License as published by the
+       Free Software Foundation; either version 2, or (at your option)
+       any later version, or
+     - the same dual license "the GNU LGPLv3+ or the GNU GPLv2+".
+
+   This file is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License and the GNU General Public License
+   for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License and of the GNU General Public License along with this
+   program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "caseprop.h"
+
+/* Quoting the Unicode standard:
+     Definition: A character is defined to be "case-ignorable" if it has the
+     value MidLetter {or the value MidNumLet} for the Word_Break property or
+     its General_Category is one of Nonspacing_Mark (Mn), Enclosing_Mark (Me),
+     Format (Cf), Modifier_Letter (Lm), or Modifier_Symbol (Sk).
+   The text marked in braces was added in Unicode 5.1.0, see
+   <https://www.unicode.org/versions/Unicode5.1.0/> section "Update of
+   Definition of case-ignorable".   */
+/* Since this predicate is only used for the "Before C" and "After C"
+   conditions of FINAL_SIGMA, we exclude the "cased" characters here.
+   This simplifies the evaluation of the regular expressions
+     \p{cased} (\p{case-ignorable})* C
+   and
+     C (\p{case-ignorable})* \p{cased}
+ */
+
+#if 0
+
+#include "unictype.h"
+#include "uniwbrk.h"
+
+bool
+uc_is_case_ignorable (ucs4_t uc)
+{
+  int wbp = uc_wordbreak_property (uc);
+
+  return (wbp == WBP_MIDLETTER || wbp == WBP_MIDNUMLET
+          || uc_is_general_category_withtable (uc, UC_CATEGORY_MASK_Mn
+                                                   | UC_CATEGORY_MASK_Me
+                                                   | UC_CATEGORY_MASK_Cf
+                                                   | UC_CATEGORY_MASK_Lm
+                                                   | UC_CATEGORY_MASK_Sk))
+         && !uc_is_cased (uc);
+}
+
+#else
+
+#include "unictype/bitmap.h"
+
+/* Define u_casing_property_case_ignorable table.  */
+#include "ignorable.h"
+
+bool
+uc_is_case_ignorable (ucs4_t uc)
+{
+  return bitmap_lookup (&u_casing_property_case_ignorable, uc);
+}
+
+#endif