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--- a/src/pathut.h
+++ b/src/pathut.h
@@ -113,6 +113,10 @@
 /// Test if path is root (x:/). root is defined by root/.. == root
 extern bool path_isroot(const std::string& p);
 
+/// Test if sub is a subdirectory of top. This is a textual test,
+/// links not allowed
+extern bool path_isdesc(const std::string& top, const std::string& sub);
+
 /// Turn absolute path into file:// url
 extern std::string path_pathtofileurl(const std::string& path);