Updated unicode escape documentation to match current implementation.
Unicode escapes were changed in [this
RFC](https://github.com/rust-lang/rfcs/blob/28aeb3c391c9afd344f124d3a69bdc2a420638b2/text/0446-es6-unicode-escapes.md)
to use the ES6 \u{00FFFF} syntax with a variable number of digits from
1-6, eliminating the need for two different syntaxes for unicode
literals.
@@ -250,8 +250,7 @@ cases mentioned in [Number literals](#number-literals) below.
##### Unicode escapes
| | Name |
|---|------|
-| `\u7FFF` | 16-bit character code (exactly 4 digits) |
-| `\U7EEEFFFF` | 32-bit character code (exactly 8 digits) |
+| `\u{7FFF}` | 24-bit Unicode character code (up to 6 digits) |
##### Numbers
@@ -286,8 +285,8 @@ raw_string : '"' raw_string_body '"' | '#' raw_string '#' ;
common_escape : '\x5c'
| 'n' | 'r' | 't' | '0'
| 'x' hex_digit 2
-unicode_escape : 'u' hex_digit 4
- | 'U' hex_digit 8 ;
+
+unicode_escape : 'u' '{' hex_digit+ 6 '}';
hex_digit : 'a' | 'b' | 'c' | 'd' | 'e' | 'f'
| 'A' | 'B' | 'C' | 'D' | 'E' | 'F'
@@ -320,12 +319,9 @@ following forms:
* An _8-bit codepoint escape_ escape starts with `U+0078` (`x`) and is
followed by exactly two _hex digits_. It denotes the Unicode codepoint
equal to the provided hex value.
-* A _16-bit codepoint escape_ starts with `U+0075` (`u`) and is followed
- by exactly four _hex digits_. It denotes the Unicode codepoint equal to
- the provided hex value.
-* A _32-bit codepoint escape_ starts with `U+0055` (`U`) and is followed
- by exactly eight _hex digits_. It denotes the Unicode codepoint equal to
- the provided hex value.
+* A _24-bit codepoint escape_ starts with `U+0075` (`u`) and is followed
+ by up to six _hex digits_ surrounded by braces `U+007B` (`{`) and `U+007D`
+ (`}`). It denotes the Unicode codepoint equal to the provided hex value.
* A _whitespace escape_ is one of the characters `U+006E` (`n`), `U+0072`
(`r`), or `U+0074` (`t`), denoting the unicode values `U+000A` (LF),
`U+000D` (CR) or `U+0009` (HT) respectively.
