Question: I want to register a sidebar but I am a little confused about the uses of the `id` argument in [`register_sidebar`](http://codex.wordpress.org/Function_Reference/register_sidebar) function.

> 
> Codex says: id - Sidebar id - Must be all in lowercase, with no spaces
>  (default is a numeric auto-incremented ID).
> 
> 
> 

Of what use is the `id` argument and must it always be in numeric form?.

Answer: 
The sidebar ID is used to uniquely identify this specific sidebar. If you don't set it and something creates another, you could find that your sidebar moves somewhere unexpected!

It doesn't need to be numeric - you can use strings, too.
Apparently, you have to avoid IDs that include prefixes from the above list as well:

e.g.:

```
#footer-xxx
#footer-yyy

```

The following setup initially worked, but resulted in errors (using the monsoon theme):

```
register_sidebar( array(
    'name'          => esc_html__( 'Footer Area', 'monsoon' ),
    'id'            => 'footer-area',
    'description'   => esc_html__( 'Appears above the footer.', 'monsoon' ),
    'before_widget' => '<div class="col-sm-3 footer-area widget %2$s">',
    'after_widget'  => '</div>',
    'before_title'  => '<h3>',
    'after_title'   => '</h3>',
) );

```

By renaming the sidebar, the errors disappeared. I haven't tested on other themes, though. So this might only be applicable to my setup.

However, thus thread really helped me in my search for a solution :)