Patch taken from
https://build.opensuse.org/projects/openSUSE:Factory/packages/html-xml-utils/files/fix-dtd-declaration.patch?rev=ea956870c438d781dcc28522afb4abf9

--- html-xml-utils-8.7/dtd.c	2025-06-28 10:44:08.062000908 +0200
+++ html-xml-utils-8.7/dtd.c	2025-06-28 10:44:31.310766962 +0200
@@ -74,8 +74,7 @@
 } ElementType;
 
 /* lookup_element -- look up the string in the hash table */
-EXPORT const ElementType * lookup_element(/* register const char *str,
-					  register unsigned int len */);
+EXPORT const ElementType * lookup_element(register const char *str, register size_t len);
 
 /* Different kinds of parent elements: */
 #define PHRASE "abbr", "acronym", "b", "bdi", "bdo", "big", "cite", "code", "dfn", "em", "i", "kbd", "q", "s", "samp", "small", "span", "strong", "sub", "sup", "time", "tt", "u", "var"