When mentioning `open` they should have noted that `open <file>` will open the given file with its associated app.
It’s indispensable.
 replies(3): 
It’s indispensable.
    open .
    firefox file.html
  alias op='open .'     function opent () {
        what=${1:-`pwd`}
        what=$(cd "$what"; pwd)
        osascript -e "tell application \"Finder\"
        activate
        set t to target of Finder window 1
        set toolbar visible of window 1 to true
        end tell
        tell application \"System Events\"
        keystroke \"t\" using command down
        end tell
        tell application \"Finder\"
        set target of Finder window 1 to POSIX file \"$what\"
        end tell" > /dev/null
    }
    ## opens current dir
    $ opent .
    ## same
    $ opent