Bad version

Each row should have 5 blocks.
"Block 6" should be on a new row, but is blocked by the big "Block 3" (because of its height).

Block 1
Block 2
Block 3 is a very long block
on several rows
that could break the layout
Block 4
Block 5
Block 6
Block 7
Block 8
Block 9
Block 10


Fixed version (using the "clear" property)

With the clear property, "Block 6" is on a new row: each row has 5 blocks cleanly aligned.

Block 1
Block 2
Block 3 is a very long block
on several rows
that could break the layout
Block 4
Block 5
Block 6
Block 7
Block 8
Block 9
Block 10