what does "if (( a & b ) == b)" mean?
if ((e.Modifiers & Keys.Shift) == Keys.Shift)
lbl.Text += "\n" + "Shift was held down.";
& -the bitwise-AND operator, which compares each bitof its first operand to the corresponding bit of its second operand. If both bits are 1, the corresponding result bit is set to 1. Otherwise, the corresponding result bit is set to 0. In this case, condition "if (( a & b ) ==b)" is TRUE, when a>=b. This construction may be used with 2-byte variables, when most significant bit is a key, least - modifiers.