No, it's more complicated
My "loads of hyphens" had many more than are being printed, so it's flicking in and out of underline mode repeatedly, but four hyphens "behaved"
-----FIVE-----
------SIX------
OK, so it'll let you have 4 hyphens, and translates that as "strike out the next two hyphens", but if you have five, it translates as "strike out the embedded single hyphen between these pairs of double hyphens"