horizWarning method
Set horizontal Warning-line to screen matrix
Implementation
void horizWarning(int _x, _y, _width, String _extraS) {
StringBuffer _b = StringBuffer();
/// form String like: ยด7777777777777777'
for (var x = 0; x < _width; x++) {
_b.write(_extraS);
}
/// Fill it to the matrix
aHeader(_x, _y, _b.toString());
}