Particles.Arcade.Emitter#alignIn()

Aligns this Group within another Game Object, or Rectangle, known as the
'container', to one of 9 possible positions.

The container must be a Game Object, or Phaser.Rectangle object. This can include properties
such as World.bounds or Camera.view, for aligning Groups within the world
and camera bounds. Or it can include other Sprites, Images, Text objects, BitmapText,
TileSprites or Buttons.

Please note that aligning a Group to another Game Object does not make it a child of
the container. It simply modifies its position coordinates so it aligns with it.

The position constants you can use are:

Phaser.TOP_LEFT, Phaser.TOP_CENTER, Phaser.TOP_RIGHT, Phaser.LEFT_CENTER,
Phaser.CENTER, Phaser.RIGHT_CENTER, Phaser.BOTTOM_LEFT,
Phaser.BOTTOM_CENTER and Phaser.BOTTOM_RIGHT.

Groups are placed in such a way that their bounds align with the
container, taking into consideration rotation and scale of its children.
This allows you to neatly align Groups, irrespective of their position value.

The optional offsetX and offsetY arguments allow you to apply extra spacing to the final
aligned position of the Group. For example:

group.alignIn(background, Phaser.BOTTOM_RIGHT, -20, -20)

Would align the group to the bottom-right, but moved 20 pixels in from the corner.
Think of the offsets as applying an adjustment to the containers bounds before the alignment takes place.
So providing a negative offset will 'shrink' the container bounds by that amount, and providing a positive
one expands it.