diff --git a/toml.abnf b/toml.abnf
index 0446f8b6..db270092 100644
--- a/toml.abnf
+++ b/toml.abnf
@@ -52,16 +52,13 @@ simple-key = quoted-key / unquoted-key
 
 ;; Unquoted key
 
-unquoted-key = 1*unquoted-key-char
-unquoted-key-char = ALPHA / DIGIT / %x2D / %x5F         ; a-z A-Z 0-9 - _
-unquoted-key-char =/ %xB2 / %xB3 / %xB9 / %xBC-BE       ; superscript digits, fractions
-unquoted-key-char =/ %xC0-D6 / %xD8-F6 / %xF8-37D       ; non-symbol chars in Latin block
-unquoted-key-char =/ %x37F-1FFF                         ; exclude GREEK QUESTION MARK, which is basically a semi-colon
-unquoted-key-char =/ %x200C-200D / %x203F-2040          ; from General Punctuation Block, include the two tie symbols and ZWNJ, ZWJ
-unquoted-key-char =/ %x2070-218F / %x2460-24FF          ; include super-/subscripts, letterlike/numberlike forms, enclosed alphanumerics
-unquoted-key-char =/ %x2C00-2FEF / %x3001-D7FF          ; skip arrows, math, box drawing etc, skip 2FF0-3000 ideographic up/down markers and spaces
-unquoted-key-char =/ %xF900-FDCF / %xFDF0-FFFD          ; skip D800-DFFF surrogate block, E000-F8FF Private Use area, FDD0-FDEF intended for process-internal use (unicode)
-unquoted-key-char =/ %x10000-EFFFF                      ; all chars outside BMP range, excluding Private Use planes (F0000-10FFFF)
+unquoted-key = 1*( ALPHA / DIGIT / %x2D / %x5F ) ; A-Z / a-z / 0-9 / - / _
+
+; These cannot be easily expressed in ABNF.
+; unquoted-key   =/ unicode-letter
+; unquoted-key   =/ unicode-digit
+; unicode-letter =  Lu / Ll / Lt / Lm / Lo ; Unicode categories
+; unicode-digit  =  Nd                     ; Unicode categories
 
 ;; Quoted and dotted key
 
diff --git a/toml.md b/toml.md
index 08cc9f67..af0e4839 100644
--- a/toml.md
+++ b/toml.md
@@ -103,14 +103,13 @@ first = "Tom" last = "Preston-Werner" # INVALID
 
 A key may be either bare, quoted, or dotted.
 
-**Bare keys** may contain any letter-like or number-like Unicode character from
-any Unicode script, as well as ASCII digits, dashes and underscores.
-Punctuation, spaces, arrows, box drawing and private use characters are not
-allowed. Note that bare keys are allowed to be composed of only ASCII digits,
-e.g. 1234, but are always interpreted as strings.
+**Bare keys** may only contain letters, digits, underscores, and dashes. Bare
+keys are allowed to be composed of only digits, e.g. `1234`, but are always
+interpreted as strings.
 
-ℹ️ The exact ranges of allowed code points can be found in the
-[ABNF grammar file][abnf].
+A "letter" is any character in the Unicode category `Lu`, `Ll`, `Lt`, `Lm`, or
+`Lo`. A "digit" is any character in the category `Nd`. Implementations must
+support at least Unicode 9.0, or optionally any later version.
 
 ```toml
 key = "value"
@@ -118,15 +117,14 @@ bare_key = "value"
 bare-key = "value"
 1234 = "value"
 Fuß = "value"
-😂 = "value"
 汉语大字典 = "value"
 辭源 = "value"
 பெண்டிரேம் = "value"
 ```
 
-**Quoted keys** follow the exact same rules as either basic strings or literal
-strings and allow you to use any Unicode character in a key name, including
-spaces. Best practice is to use bare keys except when absolutely necessary.
+**Quoted keys** follow the same rules as either basic strings or literal
+strings, and allow you to use any character in a key name including spaces. Best
+practice is to use bare keys except when absolutely necessary.
 
 ```toml
 "127.0.0.1" = "value"