Etag: weak vs strong example

I have been reading about Etags, and I understand that there are 2 ways of generating an Etag, weak and strong. Weak Etags are computationally easier to generate than strong ones. I have also come to know that Weak Etags are practically enough for most use cases.

from MDN

Weak validators are easy to generate but are far less useful for comparisons. Strong validators are ideal for comparisons but can be very difficult to generate efficiently.

another snippet:

Weak Etag values of two representations of the same resources might be semantically equivalent, but not byte-for-byte identical.

I am finding it hard to understand what does it mean for a resource to be semantically similar but not byte by byte same ? It would be great to see some examples.