Word cloud visual how to use the Exclude feature?

Thanks for the example. But could you elaborate on the role of the key column between the two tables?

For example, the Words dataset includes the words "Power BI" and "Microsoft" with keys 1 and 2 respectively. The Excludes dataset includes the words "Javascript" and "LESS" with keys 1 and 2. I would expect that the exclusion word "Javascript" is applied to "Power BI" and "LESS" is applied to "Microsoft". In that case, the exclusion list should have no effect on the word cloud. However, every word in the exclusion list seems to be applied to every word in the target dataset.

It is really hard to grasp the meaning of the key column. Although it is required, it seems that it has no effect on how the word cloud is presented? Why is it required?