Even worse is the all-decimal MAC problem.<p>Some genius decided that, to make time input convenient, YAML would parse HH:MM:SS as SS + 60×MM + 60×60×HH. So you could enter 1:23:45 and it would give you the correct number of seconds in 1 hour, 23 minutes, and 45 seconds.<p>They neglected to put a maximum on the number of such sexagesimal places, so if you put, say, six numbers separated by colons like this, it would be parsed as a very large integer.<p>Imagine my surprise when, while working at a networking company, we had some devices which failed to configure their MAC addresses in YAML! After this YAML config file had been working for literal years! (I believe this was via netplan? It's been like a decade, I don't remember.)<p>Turns out, if an unquoted MAC address had even a single non-decimal hex digit, it would do what we expected (parse as a string). This is not only by FAR the more common case, but also we had an A in our vendor prefix, so we never ran into this "feature" during initial development.<p>Then one day we ran out of MAC addresses and got a new vendor prefix. This time it didn't have any letters in it. Hilarity ensued.<p>(This behavior has thankfully been removed in more recent YAML standards.)