Replaces the account name, host name and home directory of the machine that made a value.
Other users' home paths become .../user; names equal to an owner become its placeholder; with home, that exact directory becomes ~ first.
.../user
~
The directory in env.HOME, or null when it is missing or the root.
env.HOME
Names to replace, from the env.* values in attrs; names under 3 characters stay.
env.*