Moving the mouse vertically up and down over the table should very quickly highlight each row moused over.

1^st col. & row	2^nd col. thead	3^rd col.	4^th col.	5^th col.
2^nd row	thead	abcd	abcd	abcd
22^th row	tfoot	a	b	c
3^rd row	tbody	abc	abc	abc
4^th row	tbody	ab	ab	ab
5^th row	tbody	ab	ab	ab
6^th row	tbody	ab	ab	ab
7^th row	tbody	ab	ab	ab
8^th row	tbody	ab	ab	ab
9^th row	tbody	ab	ab	ab
10^th row	tbody	ab	ab	ab
11^th row	tbody	ab	ab	ab
12^th row	tbody	ab	ab	ab
13^th row	tbody	ab	ab	ab
14^th row	tbody	ab	ab	ab
15^th row	tbody	ab	ab	ab
16^th row	tbody	ab	ab	ab
17^th row	tbody	ab	ab	ab
18^th row	tbody	ab	ab	ab
19^th row	tbody	ab	ab	ab
20^th row	tbody	ab	ab	ab
21^th row	tbody	ab	ab	ab

Background-color change when hovering over table rows with tr:hover is not snappy from Milton