This tests the animation's SMIL fill attribute.

On the first row, the <set> animation has its dur attribute set to '1s' and its begin attribute set to '0s; firstSet.end + 1s'. The fill attribute is unspecified, so the effect is as if it was set to 'remove', because 'remove' is the default value for fill. Consequently, the first interval is (0s <= t < 1s), the second is (2s <= t < 3s), the third, (4s <= t < 5s) etc.. The red rectangle starts on the right position, moves to the left position for one second, moves to the right for 1 second, and so on.

On the second row, the <set> animation with the identifier 'firstSet' has its dur attribute set to 1s and its begin attribute set to '0s; firstSet.end'. The fill attribute is set to 'remove'. The behavior should be exactly the same as for the previous row, and the rectangle moves from the right position to the left position every second.

On the third row, the <set> animation has its dur attribute set to 1s and its begin attribute set to '0s; firstSet.end'. The fill attribute is set to 'freeze'. The first interval should be (0s <= t < 1s), the second (2s <= t < 3s), the third, (4s <= t < 5s), etc. Between interval, the fill behavior should be applied, so the red rectangle should stay on the right position and never go to the left position.

On the fourth row, the <set> animation has its dur attribute set to 1s and its begin attribute set to '0s'. The fill attribute is set to 'freeze'. The first interval should be (0s <= t < 1s) and there is no following interval. Because of the fill behavior, the <set> should apply the last (and only) animation value after 1s. Consequently, the red rectangle should stay on the right position and never go to the left position.