**Emoji**aresmallimagesembeddedintext,therearetwomajortypesofemoji:[unicodeemoji](https://en.wikipedia.org/wiki/Emoji) and custom emoji. While unicode emoji are universal and standardized, they can appear differently depending on where you are using them or may not appear at all on older systems. Custom emoji are a more *fun* kind - instance administrator can define many images as *custom emoji* for their users. This works very simple - custom emoji is defined by its *shortcode* and an image, so that any shortcode enclosed in colons get replaced with image if such shortcode exist.
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