I'm aware that in Vim I can often repeat a command by simply adding a number in front of it. For example, one can delete 5 lines by:

```
5dd

```

It's also often possible to specify a range of lines to apply a command to, for example

```
:10,20s:hello:goodbye:gc

```

How can I perform a 'vertical edit'? I'd like to, for example, insert a particular symbol, say a comma, at the beggining (skipping whitespace, i.e. what you'd get if you type a comma after Shift-I in command mode) of every line in a given range. How can this be achieved (without resorting to down-period-down-period-down-period)?