Feature summary:

Expand the options at Special:Block to include an option for limiting a block to a web browser (e.g., Safari) or user-agent string.

See https://en.wikipedia.org/wiki/Wikipedia:Village_pump_(idea_lab)#Browser-specific_range_blocks (permalink)

Use case(s):

This might be most useful for reducing the scope of a range block. The block could apply to anyone who is from this large range and who is using the specified web browser.

Benefits:

This could limit collateral damage for range blocks.