<space> with a count argument replaces current selections with the counth selection.

src/main.cc

@@ -775,7 +775,8 @@ std::unordered_map<Key, std::function<void (Window& window, int count)>> keymap
 
     { { Key::Modifiers::None, ':' }, [](Window& window, int count) { do_command(); } },
     { { Key::Modifiers::None, '|' }, do_pipe },
-    { { Key::Modifiers::None, ' ' }, [](Window& window, int count) { window.clear_selections(); } },
+    { { Key::Modifiers::None, ' ' }, [](Window& window, int count) { if (count == 0) window.clear_selections();
+                                                                     else window.keep_selection(count-1); } },
     { { Key::Modifiers::None, 'w' }, [](Window& window, int count) { do { window.select(select_to_next_word); } while(--count > 0); } },
     { { Key::Modifiers::None, 'e' }, [](Window& window, int count) { do { window.select(select_to_next_word_end); } while(--count > 0); } },
     { { Key::Modifiers::None, 'b' }, [](Window& window, int count) { do { window.select(select_to_previous_word); } while(--count > 0); } },

src/window.cc

@@ -239,6 +239,18 @@ void Window::clear_selections()
     selections().push_back(std::move(sel));
 }
 
+void Window::keep_selection(int index)
+{
+    check_invariant();
+
+    if (index < selections().size())
+    {
+        Selection sel = selections()[index];
+        selections().clear();
+        selections().push_back(std::move(sel));
+    }
+}
+
 void Window::select(const Selector& selector, bool append)
 {
     check_invariant();

src/window.hh

@@ -73,6 +73,7 @@ public:
     void move_cursor_to(const BufferIterator& iterator);
 
     void clear_selections();
+    void keep_selection(int index);
     void select(const Selector& selector, bool append = false);
     void multi_select(const MultiSelector& selector);
     BufferString selection_content() const;