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# Unicode Syntax
Elixir implements [Unicode Annex #31](http://unicode.org/reports/tr31/) for non-quoted atoms and variables as specified in this document.
## Version
The specification in this document is included in Elixir v1.5 and requires OTP 20+. To check the Unicode version of your current Elixir installation, please run `String.Unicode.version()`.
## R1. Default Identifiers
Elixir identifiers are identified as:
<Identifier> := <Start> <Continue>* <Ending>?
where `<Start>` is:
> characters derived from the Unicode General Category of uppercase letters, lowercase letters, titlecase letters, modifier letters, other letters, letter numbers, plus `Other_ID_Start`, minus `Pattern_Syntax` and `Pattern_White_Space` code points
>
> In set notation: `[[:L:][:Nl:][:Other_ID_Start:]--[:Pattern_Syntax:]--[:Pattern_White_Space:]]`
and `<Continue>` is:
> ID_Start characters, plus characters having the Unicode General Category of nonspacing marks, spacing combining marks, decimal number, connector punctuation, plus `Other_ID_Continue`, minus `Pattern_Syntax` and `Pattern_White_Space` code points.
>
> In set notation: `[[:ID_Start:][:Mn:][:Mc:][:Nd:][:Pc:][:Other_ID_Continue:]--[:Pattern_Syntax:]--[:Pattern_White_Space:]]`
`<Ending>` is an addition specific to Elixir that includes the codepoints ? (003F) and ! (0021).
Elixir does not implement requirement R1a. It does implement requirement R1b.
### Atoms
Atoms in Elixir follow the identifier rule above with the following modifications:
* `<Start>` includes the codepoint _ (005F)
* `<Continue>` includes the codepoint @ (0040)
### Variables
Atoms in Elixir follow the identifier rule above with the following modifications:
* `<Start>` includes the codepoint _ (005F)
* `<Start>` must not include Lu (letter uppercase) and Lt (letter titlecase) characters
* `<Continue>` includes Lu (letter uppercase) and Lt (letter titlecase) characters
## R6. Filtered Normalized Identifiers
Identifiers in Elixir are case sensitive.
Elixir requires all atoms and variables to be in NFC form. Any other form will fail with a relevant error message. Quoted-atoms and variables can, however, be in any form and are not verified by the parser.
In other words, the atom `:josé` can only be written with the codepoints 006A 006F 0073 00E9. On the other hand, `:"josé"` may be written as 006A 006F 0073 00E9 or 006A 006F 0073 0065 0301.
## Other considerations
It is worth noting that Elixir supports only codepoints \t (0009), \n (000A), \r (000D) and \s (0020) as whitespace and therefore does not follow requirement R3.
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