Updated section on identifiers for raw identifiers

Author: Alexander Regueiro

src/identifiers.md

@@ -5,8 +5,10 @@
 > &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>
 >
+> RAW_IDENTIFIER : `r#` IDENTIFIER_OR_KEYWORD <sub>*Except `crate`, `extern`, `self`, `super`, `Self`*</sub>
+>
 > IDENTIFIER :\
-> IDENTIFIER_OR_KEYWORD <sub>*Except a [strict] or [reserved] keyword*</sub>
+> IDENTIFIER_OR_KEYWORD <sub>*Except a [strict] or [reserved] keyword*</sub> | RAW_IDENTIFIER
 
 An identifier is any nonempty ASCII string of the following form:
 
@@ -21,5 +23,10 @@ Or
 * The identifier is more than one character. `_` alone is not an identifier.
 * The remaining characters are alphanumeric or `_`.
 
+A raw identifier is like a normal identifier, but prefixed by `r#`. (Note that
+the `r#` prefix is not included as part of the actual identifier.)
+Unlike a normal identifier, a raw identifier may be any strict or reserved
+keyword except the ones listed above for `RAW_IDENTIFIER`.
+
 [strict]: keywords.html#strict-keywords
 [reserved]: keywords.html#reserved-keywords