Melchior FRANZ:

Vivian pointed out that a redefined Ctrl-U key binding didn't work
correctly. I found out that this is, because the definition in
$FG_ROOT/keyboard.xml sets <value type="bool"> for binding[1],
and ... [better sit down first!] ... and assigning <value type="double">
in a *-set.xml file doesn't *really* set "double" as new type!

Instead, the boolean is kept, and a double sqeezed into it. In other
words: once tainted as bool, you can throw all doubles in the universe
on a property node, and all it will accept is 0 and 1. Without warning!

BTW: I changed the patch: I was overly cautious: clear_value() does already
care for ties and for setting NONE, so we just need to make that public as
clearValue(), and use that. Makes the patch a bit more verbose, though.  :-/

simgear/props/props.hxx

@@ -1172,6 +1172,12 @@ public:
   void fireChildRemoved (SGPropertyNode * child);
 
 
+  /**
+   * Clear any existing value and set the type to NONE.
+   */
+  void clearValue ();
+
+
 protected:
 
   void fireValueChanged (SGPropertyNode * node);
@@ -1203,12 +1209,6 @@ private:
   bool set_string (const char * value);
 
 
-  /**
-   * Clear any existing value and set the type to NONE.
-   */
-  void clear_value ();
-
-
   /**
    * Get the value as a string.
    */