diff --git a/doomsday/libs/core/include/de/data/hash.h b/doomsday/libs/core/include/de/data/hash.h
index 58e61caf5e..7991c1e01c 100644
--- a/doomsday/libs/core/include/de/data/hash.h
+++ b/doomsday/libs/core/include/de/data/hash.h
@@ -27,10 +27,13 @@ namespace de {
  * Efficient key-value container with unordered keys (based on std::unordered_map).
  * @ingroup data
  */
-template <typename Key, typename Value>
-class Hash : public std::unordered_map<Key, Value>
+template <typename Key,
+          typename Value,
+          typename HashFn = std::hash<Key>,
+          typename KeyEqual = std::equal_to<Key>>
+class Hash : public std::unordered_map<Key, Value, HashFn, KeyEqual>
 {
-    using Base = std::unordered_map<Key, Value>;
+    using Base = std::unordered_map<Key, Value, HashFn, KeyEqual>;
 
 public:
     Hash() {}
@@ -65,30 +68,33 @@ class Hash : public std::unordered_map<Key, Value>
     }
 };
 
-template <typename Key, typename Value>
+template <typename Key,
+          typename Value,
+          typename HashFn = std::hash<Key>,
+          typename KeyEqual = std::equal_to<Key>>
 class MutableHashIterator
 {
-    using Container = Hash<Key, Value>;
+    using Container = Hash<Key, Value, HashFn, KeyEqual>;
     using Iterator = typename Container::iterator;
 
     Container _hash;
+    Iterator _iter;
     Iterator _cur;
-    Iterator _next;
 
 public:
     MutableHashIterator(Container &c) : _hash(c)
     {
-        if (!_hash.empty()) _next = c.begin();
+        _iter = _hash.begin();
     }
 
     bool hasNext() const
     {
-        return !_hash.empty() && _next != _hash.end();
+        return _iter != _hash.end();
     }
 
     Iterator &next()
     {
-        _cur = _next++;
+        _cur = _iter++;
         return _cur;
     }
 
@@ -104,7 +110,7 @@ class MutableHashIterator
 
     void remove()
     {
-        _hash.erase(_cur);
+        _iter = _hash.erase(_cur);
     }
 };
 } // namespace de
diff --git a/doomsday/libs/core/include/de/data/map.h b/doomsday/libs/core/include/de/data/map.h
index 00345dfc11..750f59aed6 100644
--- a/doomsday/libs/core/include/de/data/map.h
+++ b/doomsday/libs/core/include/de/data/map.h
@@ -26,10 +26,10 @@ namespace de {
 /**
  * Key-value container with ordered keys (based on std::map).
  */
-template <typename Key, typename Value>
-class Map : public std::map<Key, Value>
+template <typename Key, typename Value, typename Compare = std::less<Key>>
+class Map : public std::map<Key, Value, Compare>
 {
-    using Base = std::map<Key, Value>;
+    using Base = std::map<Key, Value, Compare>;
 
 public:
     Map() {}
@@ -59,31 +59,30 @@ class Map : public std::map<Key, Value>
     }
 };
 
-template <typename Key, typename Value>
+template <typename Key, typename Value, typename Compare = std::less<Key>>
 class MutableMapIterator
 {
-    using Container = Map<Key, Value>;
+    using Container = Map<Key, Value, Compare>;
     using Iterator = typename Container::iterator;
 
     Container _map;
+    Iterator _iter;
     Iterator _cur;
-    Iterator _next;
 
 public:
     MutableMapIterator(Container &c) : _map(c)
     {
-        if (!_map.empty()) _next = c.begin();
+        _iter = _map.begin();
     }
 
     bool hasNext() const
     {
-        return !_map.empty() && _next != _map.end();
+        return _iter != _map.end();
     }
 
     Iterator &next()
     {
-        _cur = _next;
-        if (hasNext()) ++_next;
+        _cur = _iter++;
         return _cur;
     }
 
@@ -99,7 +98,7 @@ class MutableMapIterator
 
     void remove()
     {
-        _map.erase(_cur);
+        _iter = _map.erase(_cur);
     }
 };
 
diff --git a/doomsday/libs/core/include/de/data/time.h b/doomsday/libs/core/include/de/data/time.h
index 6a3461edf0..a0a9f9f2a6 100644
--- a/doomsday/libs/core/include/de/data/time.h
+++ b/doomsday/libs/core/include/de/data/time.h
@@ -170,7 +170,7 @@ class DE_PUBLIC Time : public ISerializable
     Time(Time &&moved);
 
     Time(const TimePoint &tp);
-    Time(iTime time);
+    Time(const iTime &time);
 
     Time(int year, int month, int day, int hour, int minute, int second);
 
diff --git a/doomsday/libs/core/include/de/filesys/folder.h b/doomsday/libs/core/include/de/filesys/folder.h
index 8b98d7a849..6ae6f58aef 100644
--- a/doomsday/libs/core/include/de/filesys/folder.h
+++ b/doomsday/libs/core/include/de/filesys/folder.h
@@ -67,7 +67,7 @@ class DE_PUBLIC Folder : public File
     DE_ERROR(NewFileError);
 
     typedef List<Feed *> Feeds;
-    typedef Map<String, File *> Contents;
+    typedef Map<String, File *, String::InsensitiveLessThan> Contents;
 
     enum PopulationBehavior {
         PopulateFullTree       = 0x1,   ///< The full tree is populated.
diff --git a/doomsday/libs/core/src/data/time.cpp b/doomsday/libs/core/src/data/time.cpp
index 7830763e46..40698e4c46 100644
--- a/doomsday/libs/core/src/data/time.cpp
+++ b/doomsday/libs/core/src/data/time.cpp
@@ -285,7 +285,7 @@ Time::Time(int year, int month, int day, int hour, int minute, int second)
 Time::Time(const TimePoint &tp) : d(new Impl(tp))
 {}
 
-Time::Time(iTime time) : d(new Impl)
+Time::Time(const iTime &time) : d(new Impl(0 /* init as invalid */))
 {
     using namespace std::chrono;
     d->flags |= Impl::SysTime;
diff --git a/doomsday/libs/core/src/filesys/directoryfeed.cpp b/doomsday/libs/core/src/filesys/directoryfeed.cpp
index 3a4eb35ffe..76abc6b114 100644
--- a/doomsday/libs/core/src/filesys/directoryfeed.cpp
+++ b/doomsday/libs/core/src/filesys/directoryfeed.cpp
@@ -106,7 +106,6 @@ Feed::PopulatedFiles DirectoryFeed::populate(Folder const &folder)
     {
             continue;
     }
-        if (name == ".." || name.first() == '.') continue;
 
         if (isDirectory_FileInfo(i.value))
         {
diff --git a/doomsday/libs/core/src/filesys/file.cpp b/doomsday/libs/core/src/filesys/file.cpp
index c201164f35..251e9ccb8d 100644
--- a/doomsday/libs/core/src/filesys/file.cpp
+++ b/doomsday/libs/core/src/filesys/file.cpp
@@ -81,7 +81,7 @@ File::~File()
     {
         // If we own a source, get rid of it.
         delete d->source;
-        d->source = 0;
+        d->source = nullptr;
     }
     if (Folder *parentFolder = parent())
     {
diff --git a/doomsday/libs/core/src/filesys/folder.cpp b/doomsday/libs/core/src/filesys/folder.cpp
index 849a9c643d..4810ff1883 100644
--- a/doomsday/libs/core/src/filesys/folder.cpp
+++ b/doomsday/libs/core/src/filesys/folder.cpp
@@ -66,7 +66,7 @@ DE_PIMPL(Folder)
 
     void add(File *file)
     {
-        contents.insert(file->name().lower(), file);
+        contents.insert(file->name(), file);
         file->setParent(thisPublic);
     }
 
@@ -216,22 +216,21 @@ void Folder::populate(PopulationBehaviors behavior)
         DE_GUARD(this);
 
         // Prune the existing files first.
-        MutableMapIterator<String, File *> iter(d->contents);
-        while (iter.hasNext())
+        for (auto iter = d->contents.begin(); iter != d->contents.end(); )
         {
-            iter.next();
-
             // By default we will NOT prune if there are no feeds attached to the folder.
             // In this case the files were probably created manually, so we shouldn't
             // touch them.
             bool mustPrune = false;
 
-            File *file = iter.value();
+            File *file = iter->second;
             if (file->mode() & DontPrune)
             {
                 // Skip this one, it should be kept as-is until manually deleted.
+                ++iter;
                 continue;
             }
+
             Feed *originFeed = file->originFeed();
 
             // If the file has a designated feed, ask it about pruning.
@@ -245,11 +244,11 @@ void Folder::populate(PopulationBehaviors behavior)
                 // There is no designated feed, ask all feeds of this folder.
                 // If even one of the feeds thinks that the file is out of date,
                 // it will be pruned.
-                for (Feeds::iterator f = d->feeds.begin(); f != d->feeds.end(); ++f)
+                for (auto *f : d->feeds)
                 {
-                    if ((*f)->prune(*file))
+                    if (f->prune(*file))
                     {
-                        LOG_RES_XVERBOSE("Pruning %s due to non-origin feed %s", file->path() << (*f)->description());
+                        LOG_RES_XVERBOSE("Pruning %s due to non-origin feed %s", file->path() << f->description());
                         mustPrune = true;
                         break;
                     }
@@ -260,9 +259,13 @@ void Folder::populate(PopulationBehaviors behavior)
             {
                 // It needs to go.
                 file->setParent(nullptr);
-                iter.remove();
+                iter = d->contents.erase(iter);
                 delete file;
             }
+            else
+            {
+                ++iter;
+            }
         }
     }
 
@@ -283,7 +286,7 @@ void Folder::populate(PopulationBehaviors behavior)
                 if (i)
                 {
                     std::unique_ptr<File> file(i);
-                    if (!d->contents.contains(i->name().lower()))
+                    if (!d->contents.contains(i->name()))
                     {
                         d->add(file.release());
                         fileSystem().index(*i);
@@ -475,7 +478,7 @@ bool Folder::has(String const &name) const
     }
 
     DE_GUARD(this);
-    return (d->contents.find(name.lower()) != d->contents.end());
+    return (d->contents.find(name) != d->contents.end());
 }
 
 File &Folder::add(File *file)
@@ -498,10 +501,8 @@ File *Folder::remove(const String &name)
 {
     DE_GUARD(this);
 
-    String const key = name.lower();
-    DE_ASSERT(d->contents.contains(key));
-
-    File *removed = d->contents.take(key);
+    DE_ASSERT(d->contents.contains(name));
+    File *removed = d->contents.take(name);
     removed->setParent(nullptr);
     return removed;
 }
@@ -520,7 +521,7 @@ filesys::Node const *Folder::tryGetChild(String const &name) const
 {
     DE_GUARD(this);
 
-    auto found = d->contents.find(name.lower());
+    auto found = d->contents.find(name);
     if (found != d->contents.end())
     {
         return found->second;