What
Some operations take a path argument, including ones that read a file as text or bytes and ones that resolve a path. The shared check on that argument now only confirms that a path was given. Before, it also refused network locations with the message "a network location is not reached from here". That message is still used in other places.
Why
In practice, network paths such as shared network drives can now get past this check for these operations.
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The writer flagged doubt
It is not clear which feature these operations belong to, or whether network locations are now refused somewhere else instead.