+static size_t strcspn_escaped(const char *s, const char *stop)
+{
+ const char *i;
+
+ for (i = s; *i; i++) {
+ /* skip the escaped character */
+ if (i[0] == '\\' && i[1]) {
+ i++;
+ continue;
+ }
+
+ if (strchr(stop, *i))
+ break;
+ }
+ return i - s;
+}
+
+static inline int invalid_value_char(const char ch)
+{
+ if (isalnum(ch) || strchr(",-_", ch))
+ return 0;
+ return -1;
+}
+
+static char *attr_value_unescape(const char *value)
+{
+ const char *src;
+ char *dst, *ret;
+
+ ret = xmallocz(strlen(value));
+ for (src = value, dst = ret; *src; src++, dst++) {
+ if (*src == '\\') {
+ if (!src[1])
+ die(_("Escape character '\\' not allowed as "
+ "last character in attr value"));
+ src++;
+ }
+ if (invalid_value_char(*src))
+ die("cannot use '%c' for value matching", *src);
+ *dst = *src;
+ }
+ *dst = '\0';
+ return ret;
+}
+