More troff bits; if you want them elsewhere, feel free to repo copy them.

src/cmd/index/gen.key

@@ -0,0 +1,57 @@
+awk ' # gen.key
+#   Input: Each input line has one of the following two forms:
+#	string                   (tab) numlist
+#	string " %key " sort.key (tab) numlist
+#   Output: Each output line has the form:
+#	sort.key (tab) string (tab) numlist
+
+BEGIN {	FS = OFS = "\t" }
+
+/ %key / { # use sort.key if it is provided
+	   i = index($1, " %key ")
+	   print substr($1, i+6), substr($1, 1, i-1), $2
+	   next
+	 }
+
+	{ # generate sort.key (in $2, by modifying string) if it is not provided
+	$3 = $2
+	$2 = $1
+
+	#Modify sort.key
+	# Remove some troff commands
+	gsub(/\\f\(..|\\f.|\\s[+-][0-9]|\\s[0-9][0-9]?/, "", $2)
+
+	# underscore -> 0, so "foo_gorp" sorts before "food"
+	gsub(/_/, "0", $2)
+
+	# quote character is %, space character is ~
+	quoted = 0
+	if ($2 ~ /%/) {  # hide quoted literals in Q
+		quoted = 1
+		gsub(/%%/,  "QQ0QQ", $2)
+		gsub(/%\[/, "QQ1QQ", $2)
+		gsub(/%\]/, "QQ2QQ", $2)
+		gsub(/%\{/, "QQ3QQ", $2)
+		gsub(/%\}/, "QQ4QQ", $2)
+		gsub(/%~/,  "QQ5QQ", $2)
+	}
+	gsub(/%e/, "\\", $2)		# implement troff escape
+	gsub(/~/, " ", $2)		# remove tildes
+	gsub(/[%\[\]\{\}]/, "", $2)	# remove % and font-changing []{}
+	if (quoted) {  # restore literals but without escape charcter
+		gsub(/QQ0QQ/, "%", $2)
+		gsub(/QQ1QQ/, "[", $2)
+		gsub(/QQ2QQ/, "]", $2)
+		gsub(/QQ3QQ/, "{", $2)
+		gsub(/QQ4QQ/, "}", $2)
+		gsub(/QQ5QQ/, "~", $2)
+	}
+	if ($2 ~ /^[^a-zA-Z]+$/)	# purely nonalphabetic lines go first
+		$2 = "  " $2
+	else if ($2 ~ /^[0-9]/)		# lines with eading digits come next
+		$2 = " " $2
+					# otherwise whatever final.sort does
+}
+
+	{ print $2, $1, $3 } 
+' $*