'What is SSTable overlap in TWCS in Cassandra?

I am trying to understand SStable overlaps in cassandra which is not suitable for TWCS. I found references like https://thelastpickle.com/blog/2016/12/08/TWCS-part1.html but I still don't understand what overlap means and how it is caused by read repairs. Can anyone please provide a simple example that would help me to understand? Thanks



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