[expr.prim.req] Fix uses of 'unevaluated operand'

Author: jensmaurer

source/expressions.tex

@@ -2621,8 +2621,6 @@
 \pnum
 A \grammarterm{requires-expression} is a prvalue of type \tcode{bool}
 whose value is described below.
-Expressions appearing within a \grammarterm{requirement-body}
-are unevaluated operands\iref{expr.prop}.
 
 \pnum
 \begin{example}
@@ -2706,6 +2704,7 @@
 \pnum
 A \grammarterm{simple-requirement} asserts
 the validity of an \grammarterm{expression}.
+The \grammarterm{expression} is an unevaluated operand\iref{expr.context}.
 \begin{note}
 The enclosing \grammarterm{requires-expression} will evaluate to \keyword{false}
 if substitution of template arguments into the \grammarterm{expression} fails.
@@ -2775,7 +2774,9 @@
 
 \pnum
 A \grammarterm{compound-requirement} asserts properties
-of the \grammarterm{expression} $E$. Substitution
+of the \grammarterm{expression} $E$.
+The \grammarterm{expression} is an unevaluated operand\iref{expr.context}.
+Substitution
 of template arguments (if any) and verification of
 semantic properties proceed in the following order:
 
@@ -2884,8 +2885,9 @@
 \end{example}
 
 \pnum
-A local parameter shall only appear as an unevaluated operand\iref{expr.prop}
-within the \grammarterm{constraint-expression}.
+Within the \grammarterm{constraint-expression},
+an \grammarterm{unqualified-id} naming a local parameter shall not be
+potentially evaluated\iref{basic.def.odr}.
 \begin{example}
 \begin{codeblock}
 template<typename T> concept C = requires (T a) {