arrays within the $_POST and $_GET arrays?

[zeb]

When would there ever be an array stored within one of the $POST or $GET keys? I ran accross this code which is part of a larger function to clean the incoming form data values, and I can't figure out when there would ever be an array stored within one of these arrays, nor could I figure out why it would be important to run the key for that array through the given clean_key function:

if ( is_array( $_GET ) )
	{
	foreach ( $_GET as $key => $val )
		{
		if ( is_array( $_GET[ $key ] ) )
			{
			foreach ( $_GET[ $key ] as $key2 => $val2 )
				{
				$output[ $key ][ clean_key($key2) ] = clean_value($val2);
				}
			}
		else
			{
			$output[ $key ] = clean_value($val);
			}
		}
	}

if( is_array( $_POST ) )
	{
	foreach ( $_POST as $key => $val )
		{
		if ( is_array( $_POST[ $key ] ) )
			{
			foreach ( $_POST[ $key ] as $key2 => $val2 )
				{
				$output[ $key ][ clean_key($key2) ] = clean_value($val2);
				}
			}
		else
			{
			$output[ $key ] = clean_value($val);
			}
		}
	}

function clean_key($key)
	{
    if ($key == '')
    	{
    	return '';
    	}
	$key = preg_replace( "/\.\./"           , ""  , $key );
	$key = preg_replace( "/\_\_(.+?)\_\_/"  , ""  , $key );
	$key = preg_replace( "/^([\w\.\-\_]+)$/", "a$1", $key );

return $key;
}

[LordShryku]

Well, when you have a multiple selection box or multiple checkbox, it would come across as an array. And you can specify array keys, so the cleaning is probably just a failsafe. These, for example, would be arrays:

<input type="text" name="text[blah]" />

<select multiple name="select[]">
   <option>Blah</option>
   <option>Blah2</option>
</select>

<input type="checkbox" name="checks[1]" value="1" />
<input type="checkbox name="checks[2]" value="2" />

[zeb]

I see. I didn't realize that you could have forms submit values as arrays. So, the regex strips out '..' and '*'... I wonder why?