;doc: update help

hledger/Hledger/Cli/Commands/Register.md

@@ -16,8 +16,9 @@ Flags:
                             description closest to DESC
   -r --related              show postings' siblings instead
      --invert               display all amounts with reversed sign
-     --sort=FIELDS          comma-separated list of fields used to sort
-                            transactions
+     --sort=FIELDS          sort by: date, desc, account, amount, absamount,
+                            or a comma-separated combination of these. For a
+                            descending sort, prefix with -. (Default: date)
   -w --width=N              set output width (default: terminal width or
                             $COLUMNS). -wN,M sets description width as well.
      --align-all            guarantee alignment across all lines (slower)

hledger/Hledger/Cli/Commands/Register.txt

@@ -15,6 +15,9 @@ Flags:
                             description closest to DESC
   -r --related              show postings' siblings instead
      --invert               display all amounts with reversed sign
+     --sort=FIELDS          sort by: date, desc, account, amount, absamount,
+                            or a comma-separated combination of these. For a
+                            descending sort, prefix with -. (Default: date)
   -w --width=N              set output width (default: terminal width or
                             $COLUMNS). -wN,M sets description width as well.
      --align-all            guarantee alignment across all lines (slower)
@@ -73,6 +76,13 @@ income account where amounts are normally displayed as negative numbers.
 It's also useful to show postings on the checking account together with
 the related account:
 
+The --sort=FIELDS flag sorts by the fields given, which can be any of
+account, amount, absamount, date, or desc/description, optionally
+separated by commas. For example, --sort account,amount will group all
+transactions in each account, sorted by transaction amount. Each field
+can be negated by a preceding -, so --sort -amount will show
+transactions ordered from smallest amount to largest amount.
+
 $ hledger register --related --invert assets:checking
 
 With a reporting interval, register shows summary postings, one per