[temp.variadic] Clarify what the elements of pack expansions are.

Also some minor wording cleanups: strike a stray "identifier" and
make paragraph 3 properly parallel to paragraphs 1 and 2.

Author: zygoloid

source/templates.tex

@@ -2539,7 +2539,7 @@
 
 \pnum
 An \defnx{\grammarterm{init-capture} pack}{init-capture pack@\fakegrammarterm{init-capture} pack}
-introduces an \grammarterm{init-capture}
+is a lambda capture that introduces an \grammarterm{init-capture}
 for each of the elements in the pack expansion of its \grammarterm{initializer}.
 \begin{example}
 \begin{codeblock}
@@ -2562,7 +2562,7 @@
 or an \grammarterm{init-capture} pack.
 The number of elements of a template parameter pack
 or a function parameter pack
-is the number of arguments provided for the parameter pack \grammarterm{identifier}.
+is the number of arguments provided for the parameter pack.
 The number of elements of an \grammarterm{init-capture} pack
 is the number of elements in the pack expansion of its \grammarterm{initializer}.
 
@@ -2681,37 +2681,40 @@
 that is neither a \tcode{sizeof...} expression
 nor a \grammarterm{fold-expression}
 produces a
-list
-$\mathtt{E}_1, \mathtt{E}_2, \dotsc, \mathtt{E}_N$,
+list of elements
+$\mathtt{E}_1,$ $\mathtt{E}_2,$ $\cdots,$ $\mathtt{E}_N$,
 where
 $N$ is the number of elements in the pack expansion parameters. Each
 $\mathtt{E}_i$ is generated by instantiating the pattern and
-replacing each pack expansion parameter with its $i$th element.
+replacing each pack expansion parameter with its $i^{\textrm{th}}$ element.
 Such an element, in the context of the instantiation, is interpreted as
 follows:
 
 \begin{itemize}
 \item
 if the pack is a template parameter pack, the element is a template
 parameter\iref{temp.param} of the corresponding kind (type or
-non-type) designating the type or value from the template
-argument;
+non-type) designating the $i^{\textrm{th}}$
+corresponding type or value template argument;
 
 \item
 if the pack is a function parameter pack, the element is an
 \grammarterm{id-expression}
-designating the function parameter that resulted from
-the instantiation of the pattern where the pack is declared;
+designating the $i^{\textrm{th}}$ function parameter
+that resulted from instantiation of
+the function parameter pack declaration;
 otherwise
 
 \item
 if the pack is an \grammarterm{init-capture} pack,
 the element is an \grammarterm{id-expression}
-designating the variable declared by the \grammarterm{init-capture}
-that resulted from the instantiation of the pattern where the pack is declared.
+designating the variable introduced by
+the $i^{\textrm{th}}$ \grammarterm{init-capture}
+that resulted from instantiation of
+the \grammarterm{init-capture} pack.
 \end{itemize}
 
-All of the $\mathtt{E}_i$ become elements in the enclosing list.
+All of the $\mathtt{E}_i$ become items in the enclosing list.
 \begin{note} The variety of list varies with the context:
 \grammarterm{expression-list},
 \grammarterm{base-specifier-list},