Merge pull request rust-lang#111 from brauliobz/grammar_identifiers

Non-ASCII chars in identifiers aren't supported yet

src/identifiers.md

@@ -2,32 +2,20 @@
 
 > **<sup>Lexer:<sup>**  
 > IDENTIFIER :  
-> &nbsp;&nbsp; &nbsp;&nbsp; XID_start XID_continue<sup>\*</sup>  
-> &nbsp;&nbsp; | `_` XID_continue<sup>+</sup>  
+> &nbsp;&nbsp; &nbsp;&nbsp; [`a`-`z` `A`-`Z`]&nbsp;[`a`-`z` `A`-`Z` `0`-`9` `_`]<sup>\*</sup>  
+> &nbsp;&nbsp; | `_` [`a`-`z` `A`-`Z` `0`-`9` `_`]<sup>+</sup>  
 
-An identifier is any nonempty Unicode[^non_ascii_idents] string of the following form:
+An identifier is any nonempty ASCII[^non_ascii_idents] string of the following form:
 
 Either
 
-   * The first character has property [`XID_start`]
-   * The remaining characters have property [`XID_continue`]
+   * The first character is a letter
+   * The remaining characters are alphanumeric or `_`
 
 Or
 
    * The first character is `_`
    * The identifier is more than one character, `_` alone is not an identifier
-   * The remaining characters have property [`XID_continue`]
+   * The remaining characters are alphanumeric or `_`
 
-that does _not_ occur in the set of [keywords].
-
-> **Note**: [`XID_start`] and [`XID_continue`] as character properties cover the
-> character ranges used to form the more familiar C and Java language-family
-> identifiers.
-
-
-
-[`XID_start`]:  http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Start%3A%5D&abb=on&g=&i=
-[`XID_continue`]: http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Continue%3A%5D&abb=on&g=&i=
-[keywords]: keywords.html
-[^non_ascii_idents]: Non-ASCII characters in identifiers are currently feature
-  gated. This is expected to improve soon.
+[^non_ascii_idents] Non-ASCII characters in identifiers are currently feature-gated. See [issue #28979](https://github.com/rust-lang/rust/issues/28979).