[fs.path.generic] Move descriptions of grammar elements out of the

grammar and into separate paragraphs, and format path grammar as we
format the language grammar.

Also rephrase description of root-name to use the defined term
"implementation-defined" directly rather than separating it into
"implementations [...] define".

Author: zygoloid

source/iostreams.tex

@@ -10646,6 +10646,9 @@
 
 \rSec3[fs.path.generic]{Generic pathname format}
 
+\def\impldefrootname{\impldef{supported \grammarterm{root-name}{s} in addition to
+any operating system dependent \grammarterm{root-name}{s}}}
+
 \begin{ncbnf}
 \nontermdef{pathname}\br
     root-name root-directory\opt relative-path\opt\br
@@ -10655,21 +10658,8 @@
 
 \begin{ncbnf}
 \nontermdef{root-name}\br
-\textnormal{An operating system dependent name identifying the
-starting location for pathname resolution~(\ref{fs.def.pathres}).
-If the operating system does not define at least one \grammarterm{root-name},
-then the implementation defines a \grammarterm{root-name}.
-Implementations are permitted to define additional \grammarterm{root-name}{s}.
-\begin{note} Many operating systems define a name
-beginning with two \grammarterm{directory-separator} characters
-as a \grammarterm{root-name} that identifies
-network or other resource locations.
-Some operating systems
-define a single letter followed by a colon
-as a drive specifier -- a \grammarterm{root-name}
-identifying a specific device such as a disk drive.
-\end{note}
-}
+    \textnormal{operating system dependent sequences of characters}\br
+    \textnormal{\impldefrootname{} sequences of characters}
 \end{ncbnf}
 
 \begin{ncbnf}
@@ -10687,17 +10677,7 @@
 
 \begin{ncbnf}
 \nontermdef{filename}\br
-    \textnormal{A non-empty sequence of characters other than \grammarterm{directory-separator} characters.
-\begin{note}
-Operating systems often place restrictions
-on the characters that may be used in a \grammarterm{filename}.
-For wide portability, users may wish to limit \grammarterm{filename}
-characters to the POSIX Portable Filename Character Set: \\
-\tcode{A B C D E F G H I J K L M N O P Q R S T U V W X Y Z} \\
-\tcode{a b c d e f g h i j k l m n o p q r s t u v w x y z} \\
-\tcode{0 1 2 3 4 5 6 7 8 9 . _ -}
-\end{note}
-}
+    \textnormal{non-empty sequence of characters other than \grammarterm{directory-separator} characters}
 \end{ncbnf}
 
 \begin{ncbnf}
@@ -10710,14 +10690,25 @@
 
 \begin{ncbnf}
 \nontermdef{preferred-separator}\br
-    \textnormal{An operating system dependent directory separator character. May be a synonym for \grammarterm{slash}.}
+    \textnormal{operating system dependent directory separator character\footnote{May be a synonym for \grammarterm{slash}.}}
 \end{ncbnf}
 
 \begin{ncbnf}
 \nontermdef{slash}\br
-    \textnormal{The slash character (\tcode{/}).}
+    \tcode{/}
 \end{ncbnf}
 
+\pnum
+\begin{note}
+Operating systems often place restrictions
+on the characters that may be used in a \grammarterm{filename}.
+For wide portability, users may wish to limit \grammarterm{filename}
+characters to the POSIX Portable Filename Character Set: \\
+\tcode{A B C D E F G H I J K L M N O P Q R S T U V W X Y Z} \\
+\tcode{a b c d e f g h i j k l m n o p q r s t u v w x y z} \\
+\tcode{0 1 2 3 4 5 6 7 8 9 . _ -}
+\end{note}
+
 \pnum
 Except in a \grammarterm{root-name},
 multiple successive \grammarterm{directory-separator} characters are considered to
@@ -10730,6 +10721,21 @@
 relative to \grammarterm{root-directory} is \impldef{meaning of \grammarterm{dot-dot} in \grammarterm{root-directory}}.
 Specific filenames may have special meanings for a particular operating system.
 
+\pnum
+A \grammarterm{root-name} identifies the
+starting location for pathname resolution~(\ref{fs.def.pathres}).
+If there are no operating system dependent \grammarterm{root-name}{s},
+at least one \impldefrootname{} \grammarterm{root-name} is required.
+\begin{note} Many operating systems define a name
+beginning with two \grammarterm{directory-separator} characters
+as a \grammarterm{root-name} that identifies
+network or other resource locations.
+Some operating systems
+define a single letter followed by a colon
+as a drive specifier -- a \grammarterm{root-name}
+identifying a specific device such as a disk drive.
+\end{note}
+
 \pnum
 If a \grammarterm{root-name} is otherwise ambiguous,
 the possibility with the longest sequence of characters is chosen.