What is the unicode variation selector

Question

I was wondering. What is the unicode Variation Selectors U-FE00 to U-FE0F used for.

Example: ︀︁︂︂ 

Answer 1

This is not a complete answer to the question, but it's pertinent to Emojis and Variant Selectors:

The ❤ character _{(U+2764 code point)} is a Unicode character from 1993.
But the ❤️ emoji is actually the ❤ (U+2764) character followed by the Variant Selector-16 (U+FE0F).

Why?

Exclusively speaking about Emojis (documentation):

VS15 and VS16 are reserved to determine whether or not a character should be displayed as an emoji. [...]
Emoji variation sequences contain VS16 (U+FE0F) for emoji-style (with color) or VS15 (U+FE0E) for text style (monochrome)

If there is a character (or symbol, glyph, etc...) that is intended to be also a emoji, the Variant Selector-16 will specify to the render, to renders it as Emoji. But if the same character is followed by the Variant Selector-15, it will specify to the render, to renders it as just text. If no Variant Selector is appended, than the default representation will depends on Unicode's specification. For Emoticons the default is Emoji. For other characters like ❤, the default is text...

Another example from Emoticons (Unicode_block)'s documentation:

Each emoticon has two variants:

U+FE0E (VARIATION SELECTOR-15) selects text presentation (e.g.