character-repertoire issues

Signed-off-by: Tim Bray <tbray@textuality.com>

draft-ietf-jsonpath-base.md

@@ -175,7 +175,7 @@ companion to, JSON Pointer {{RFC6901}}. See {{json-pointer}}.
 
 The grammatical rules in this document are to be interpreted as ABNF,
 as described in {{-abnf}}.
-ABNF terminal values in this document define Unicode code points rather than
+ABNF terminal values in this document define Unicode scalar values rather than
 their UTF-8 encoding.
 For example, the Unicode PLACE OF INTEREST SIGN (U+2318) would be defined
 in ABNF as `%x2318`.
@@ -526,7 +526,7 @@ these nodes as a nodelist.
 
 A query MUST be encoded using UTF-8.
 The grammar for queries given in this document assumes that its UTF-8 form is first decoded into
-Unicode code points as described
+Unicode scalar valuess as described
 in {{RFC3629}}; implementation approaches that lead to an equivalent
 result are possible.
 
@@ -831,6 +831,12 @@ sequences of Unicode scalar values. In other words, normalization operations
 MUST NOT be applied to either the member name string `M` from the JSONPath or to
 the member name strings in the JSON prior to comparison.
 
+Note that the "\u" Unicode character escape is dissimilar from the
+same escape mechanism in JSON. In JSON, Unicode scalar values greater than
+U+FFFF are given in two \u escapes, each carrying one UTF-16 surrogate
+code point.  In JSON, U+1F609 WINKING FACE EMOJI would be represented
+as \uD83D\uDE09, but in JSONPath it would just be be \u1F609.
+
 #### Examples
 
 <!-- EDITING NOTE: there are non-breaking spaces here between j and j -->
@@ -1808,7 +1814,8 @@ bracketed-selection = "[" S selector *(S "," S selector) S "]"
 member-name-shorthand = name-first *name-char
 name-first          = ALPHA /
                       "_"   /
-                      %x80-10FFFF   ; any non-ASCII Unicode character
+                      %x7E-D7FF /   ; skip surrogate code points
+                      %xE000-10FFFF
 name-char           = DIGIT / name-first
 
 DIGIT               = %x30-39              ; 0-9