code: func (st StackTrace) Format(s fmt.State, verb rune) {
  	switch verb {
  	case 'v':
  		switch {
  		case s.Flag('+'):
  			for _, f := range st {
  				io.WriteString(s, "\n")
  				f.Format(s, verb)
  			}
  		case s.Flag('#'):
  			fmt.Fprintf(s, "%#v", []Frame(st))
  		default:
  			st.formatSlice(s, verb)
  		}
  	case 's':
  		st.formatSlice(s, verb)
  	}
  }
docs: // Format formats the stack of Frames according to the fmt.Formatter interface.
  //
  //    %s	lists source files for each Frame in the stack
  //    %v	lists the source file and line number for each Frame in the stack
  //
  // Format accepts flags that alter the printing of some verbs, as follows:
  //
  //    %+v   Prints filename, function, and line number for each Frame in the stack.