+void *xrealloc(void *ptr, size_t sz);
+
+const char **load_filters(unsigned flags, const char *first, ...);
+#define LOADF_MUST 1u
+#define LF_END ((const char *)0)
+
+void filter_environment(unsigned flags, const char *prefix_in,
+ const char *const *patv,
+ const char *const *defaults,
+ void (*foundone)(const char *fulln, const char *en,
+ const char *ev, void *p),
+ void *p);
+#define FILTF_WILDCARD 1u