...
  // identifiers of methods currently supported by intrinsic behaviors,
  // see function HTMLayoutCallMethod 

  enum BEHAVIOR_METHOD_IDENTIFIERS
  {
    DO_CLICK = 0,
    GET_TEXT_VALUE = 1,
    SET_TEXT_VALUE,
      // p - TEXT_VALUE_PARAMS
    
    TEXT_EDIT_GET_SELECTION,
      // p - TEXT_EDIT_SELECTION_PARAMS

    TEXT_EDIT_SET_SELECTION,
      // p - TEXT_EDIT_SELECTION_PARAMS

    // Replace selection content or insert text at current caret position.
    // Replaced text will be selected. 
    TEXT_EDIT_REPLACE_SELECTION, 
      // p - TEXT_EDIT_REPLACE_SELECTION_PARAMS

    // Set value of type="vscrollbar"/"hscrollbar"
    SCROLL_BAR_GET_VALUE,
    SCROLL_BAR_SET_VALUE,

    // get current caret position, it returns rectangle that is relative to origin of the editing element.
    TEXT_EDIT_GET_CARET_POSITION,
      // p - TEXT_CARET_POSITION_PARAMS

    TEXT_EDIT_GET_SELECTION_TEXT, // p - TEXT_SELECTION_PARAMS, OutputStreamProc will receive stream of WCHARs
    TEXT_EDIT_GET_SELECTION_HTML, // p - TEXT_SELECTION_PARAMS, OutputStreamProc will receive stream of BYTEs - utf8 encoded html fragment.
    TEXT_EDIT_CHAR_POS_AT_XY,     // p - TEXT_EDIT_CHAR_POS_AT_XY_PARAMS

    IS_EMPTY      = 0xFC,       // p - IS_EMPTY_PARAMS // set VALUE_PARAMS::is_empty (false/true) reflects :empty state of the element.
    GET_VALUE     = 0xFD,       // p - VALUE_PARAMS 
    SET_VALUE     = 0xFE,       // p - VALUE_PARAMS 

    XCALL                       = 0xFF, // p - XCALL_PARAMS
    FIRST_APPLICATION_METHOD_ID = 0x100 
  };
...
  struct TEXT_EDIT_CHAR_POS_AT_XY_PARAMS: METHOD_PARAMS
  {
    INT x,y;         // in
    INT      char_pos;   // out
    HELEMENT he;     // out
    int      he_pos; // out
    TEXT_EDIT_CHAR_POS_AT_XY_PARAMS() { methodID = TEXT_EDIT_CHAR_POS_AT_XY; }
  };
...

...
    class editbox: public element
    {
        
      public: 
        ...
        int char_pos_at_xy(int x, int y) const
        {
          TEXT_EDIT_CHAR_POS_AT_XY_PARAMS sp;
          sp.x = x;
          sp.y = y;
          if(!const_cast<editbox*>(this)->call_behavior_method(&sp))
            return -1;
          return sp.char_pos;
        }
    };
...