CWG2870 Combining absent encoding-prefixes

Author: burblebee

source/lex.tex

@@ -1901,16 +1901,11 @@
 
 \pnum
 \indextext{concatenation!string}%
-The common \grammarterm{encoding-prefix}
-for a sequence of adjacent \grammarterm{string-literal}s
-is determined pairwise as follows.
-If two \grammarterm{string-literal}{s} have
-the same \grammarterm{encoding-prefix},
-the common \grammarterm{encoding-prefix} is that \grammarterm{encoding-prefix}.
-If one \grammarterm{string-literal} has no \grammarterm{encoding-prefix},
-the common \grammarterm{encoding-prefix} is that
-of the other \grammarterm{string-literal}.
-Any other combinations are ill-formed.
+The \grammarterm{string-literal}{s} in
+any sequence of adjacent \grammarterm{string-literal}{s}
+shall have at most one unique \grammarterm{encoding-prefix} among them.
+The common \grammarterm{encoding-prefix} of the sequence is
+that \grammarterm{encoding-prefix}, if any.
 \begin{note}
 A \grammarterm{string-literal}'s rawness has
 no effect on the determination of the common \grammarterm{encoding-prefix}.