Dynamic Minimum width with Format / writefln

[Chris Katko]

  - First, I'm confused. The docs say 's' is "whatever it needs to 
be". ("he corresponding argument is formatted in a manner 
consistent with its type:") But what if I specifically want a 
STRING. Because I only see floats, ints, etc. No forced string 
types.

  - Second,

This works fine in D:

     printf("%-*s|", col.width-1, col.name.toStringz());

It's a left-aligned, string with a minimum width from the first 
argument, col.width. (-1 because I'm throwing a pipe symbol on 
the end.)

Now with writefln:

     writefln("%-*s|", col.width-1, col.name);

Same format specifier, except I don't need a toStringz which is 
nice. Except it doesn't work and tries to decode col.width-1 into 
a hexadecimal number and only prints that. ("4D6EF6")

I looked through the docs:

https://dlang.org/phobos/std_format.html

  '%' Position Flags Width Separator Precision FormatChar

Width:
     empty
     Integer
     '*'

But there are then zero examples or explanations of how to use 
that option. What's going on here?