src/doc/reference/src/identifiers.md

   1 # Identifiers
   2
   3 > **<sup>Lexer:<sup>**
   4 > IDENTIFIER :
   5 > &nbsp;&nbsp; &nbsp;&nbsp; XID_start XID_continue<sup>\*</sup>
   6 > &nbsp;&nbsp; | `_` XID_continue<sup>+</sup>
   7
   8 An identifier is any nonempty Unicode[^non_ascii_idents] string of the following form:
   9
  10 Either
  11
  12    * The first character has property [`XID_start`]
  13    * The remaining characters have property [`XID_continue`]
  14
  15 Or
  16
  17    * The first character is `_`
  18    * The identifier is more than one character, `_` alone is not an identifier
  19    * The remaining characters have property [`XID_continue`]
  20
  21 that does _not_ occur in the set of [keywords].
  22
  23 > **Note**: [`XID_start`] and [`XID_continue`] as character properties cover the
  24 > character ranges used to form the more familiar C and Java language-family
  25 > identifiers.
  26
  27
  28
  29 [`XID_start`]:  http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Start%3A%5D&abb=on&g=&i=
  30 [`XID_continue`]: http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Continue%3A%5D&abb=on&g=&i=
  31 [keywords]: keywords.html
  32 [^non_ascii_idents]: Non-ASCII characters in identifiers are currently feature
  33   gated. This is expected to improve soon.