Notepad++ should work now.

scintilla_messages.h

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+#pragma once
+#include <stddef.h>
+
+// Public Scintilla API: https://www.scintilla.org/ScintillaDoc.html
+// Positions are encoded byte offsets, not UTF-16 offsets.
+#define SCI_GETLENGTH 2006
+#define SCI_GETCHARAT 2007
+#define SCI_GETCURRENTPOS 2008
+#define SCI_GETANCHOR 2009
+#define SCI_GETTEXTRANGEFULL 2039
+#define SCI_GETLINEENDPOSITION 2136
+#define SCI_GETCODEPAGE 2137
+#define SCI_GETREADONLY 2140
+#define SCI_SETSEL 2160
+#define SCI_LINEFROMPOSITION 2166
+#define SCI_POSITIONFROMLINE 2167
+#define SCI_CUT 2177
+#define SCI_CLEAR 2180
+#define SCI_WORDENDPOSITION 2267
+#define SCI_SELECTIONISRECTANGLE 2372
+#define SCI_POSITIONBEFORE 2417
+#define SCI_POSITIONAFTER 2418
+#define SCI_STYLEGETCHARACTERSET 2490
+#define SCI_GETSELECTIONS 2570
+
+typedef struct ScintillaTextRange {
+  struct { ptrdiff_t start, end; } range;
+  char *text;
+} ScintillaTextRange;