Comment to getFieldstrength() added about return value

src/Classic/Fields/Fieldmap.h

@@ -71,6 +71,7 @@ public:
 
     static std::string typeset_msg(const std::string &msg, const std::string &title);
 
+    // Note: getFieldstrength() returns true if R is outside of the field!
     virtual bool getFieldstrength(const Vector_t &R, Vector_t &E, Vector_t &B) const = 0;
     virtual bool getFieldDerivative(const Vector_t &R, Vector_t &E, Vector_t &B, const DiffDirection &dir) const = 0;
     virtual void getFieldDimensions(double &zBegin, double &zEnd, double &rBegin, double &rEnd) const = 0;