diff --git a/src/pricehist/outputs/beancount.py b/src/pricehist/outputs/beancount.py
index 5be3711..366cc86 100644
--- a/src/pricehist/outputs/beancount.py
+++ b/src/pricehist/outputs/beancount.py
@@ -1,3 +1,25 @@
+"""
+Beancount output
+
+Supports the `Beancount <https://beancount.github.io/>`_ plain text accounting
+format.
+
+The default output should be valid for Beancount. Customizing it via formatting
+options may generate invalid output, so users should keep the requirements of
+the Beancount format in mind.
+
+Relevant sections of the Beancount documentation:
+
+* `Commodities / Currencies <https://beancount.github.io/docs/beancount_language_syntax.html#commodities-currencies>`_
+* `Prices <https://beancount.github.io/docs/beancount_language_syntax.html#prices>`_
+* `Fetching Prices in Beancount <https://beancount.github.io/docs/fetching_prices_in_beancount.html>`_
+
+Classes:
+
+    Beancount
+
+"""
+
 from pricehist.format import Format
 
 from .baseoutput import BaseOutput
@@ -7,19 +29,9 @@ class Beancount(BaseOutput):
     def format(self, series, source=None, fmt=Format()):
         output = ""
         for price in series.prices:
-            # TODO warn if fmt settings make an invalid number (not . for decimal)
-            # TODO warn if fmt settings make an invalid quote (not right/rightspace)
             date = fmt.format_date(price.date)
             base = fmt.base or series.base
             quote = fmt.quote or series.quote
             quote_amount = fmt.format_quote_amount(quote, price.amount)
             output += f"{date} price {base} {quote_amount}\n"
         return output
-
-
-# NOTE: Beancount always has commodity to the right. It seems to be possible to
-# skip the space, according to https://plaintextaccounting.org/quickref/#h.n4b87oz9ku6t
-
-# https://beancount.github.io/docs/fetching_prices_in_beancount.html
-# https://beancount.github.io/docs/beancount_language_syntax.html#commodities-currencies
-# https://beancount.github.io/docs/beancount_language_syntax.html#comments
diff --git a/src/pricehist/outputs/csv.py b/src/pricehist/outputs/csv.py
index 14fc101..0a63f4a 100644
--- a/src/pricehist/outputs/csv.py
+++ b/src/pricehist/outputs/csv.py
@@ -1,3 +1,20 @@
+"""
+CSV output
+
+Comma Separated Values output is easily processed with other command-line tools
+or imported into a spreadsheet or database.
+
+Python's `csv <https://docs.python.org/3/library/csv.html>`_ module is used to
+produce Excel-style CSV output, except with UNIX-style line endings. The field
+delimiter can be set with a formatting option, and date, number and base/quote
+formatting options will be respected.
+
+Classes:
+
+    CSV
+
+"""
+
 import csv
 import io
 
@@ -7,7 +24,7 @@ from .baseoutput import BaseOutput
 
 
 class CSV(BaseOutput):
-    def format(self, series, source=None, fmt=Format()):
+    def format(self, series, source, fmt=Format()):
         output = io.StringIO()
         writer = csv.writer(
             output,
diff --git a/src/pricehist/outputs/gnucashsql.py b/src/pricehist/outputs/gnucashsql.py
index abffb20..0701908 100644
--- a/src/pricehist/outputs/gnucashsql.py
+++ b/src/pricehist/outputs/gnucashsql.py
@@ -51,10 +51,10 @@ from .baseoutput import BaseOutput
 
 
 class GnuCashSQL(BaseOutput):
-    def format(self, series, source=None, fmt=Format()):
+    def format(self, series, source, fmt=Format()):
         base = fmt.base or series.base
         quote = fmt.quote or series.quote
-        src = f"pricehist:{source.id()}"
+        src = source.id()
 
         self._warn_about_backslashes(
             {
@@ -150,10 +150,10 @@ class GnuCashSQL(BaseOutput):
 
     def _sql_str(self, s):
         # Documentation regarding SQL string literals:
-        # - https://www.sqlite.org/lang_expr.html#literal_values_constants_
-        # - https://mariadb.com/kb/en/string-literals/
-        # - https://dev.mysql.com/doc/refman/8.0/en/string-literals.html
-        # - https://www.postgresql.org/docs/devel/sql-syntax-lexical.html
+        # * https://www.sqlite.org/lang_expr.html#literal_values_constants_
+        # * https://mariadb.com/kb/en/string-literals/
+        # * https://dev.mysql.com/doc/refman/8.0/en/string-literals.html
+        # * https://www.postgresql.org/docs/devel/sql-syntax-lexical.html
         escaped = s.replace("'", "''")
         quoted = f"'{escaped}'"
         return quoted
diff --git a/src/pricehist/outputs/ledger.py b/src/pricehist/outputs/ledger.py
index 054c998..6682677 100644
--- a/src/pricehist/outputs/ledger.py
+++ b/src/pricehist/outputs/ledger.py
@@ -1,3 +1,30 @@
+"""
+Ledger output
+
+Supports both `Ledger <https://www.ledger-cli.org/>`_ and
+`hledger <https://hledger.org/>`_ plain text accounting formats.
+
+By default the output should be valid for Ledger, but can be customized for
+hledger or other variants via formatting options. Invalid variants are
+possible, so the user should be familiar with the requirements of the target
+format.
+
+Relevant sections of the Ledger manual:
+
+* `Commodities and Currencies <https://www.ledger-cli.org/3.0/doc/ledger3.html#Commodities-and-Currencies>`_
+* `Commoditized Amounts <https://www.ledger-cli.org/3.0/doc/ledger3.html#Commoditized-Amounts>`_
+
+Relevant sections of the hledger manual:
+
+* `Declaring market prices <https://hledger.org/hledger.html#declaring-market-prices>`_:
+* `Declaring commodities <https://hledger.org/hledger.html#declaring-commodities`_:
+
+Classes:
+
+    Ledger
+
+"""
+
 from pricehist.format import Format
 
 from .baseoutput import BaseOutput
@@ -11,26 +38,6 @@ class Ledger(BaseOutput):
             base = fmt.base or series.base
             quote = fmt.quote or series.quote
             quote_amount = fmt.format_quote_amount(quote, price.amount)
-            output += f"P {date} {fmt.time} {base} {quote_amount}\n"
+            timesep = " " if fmt.time else ""
+            output += f"P {date}{timesep}{fmt.time} {base} {quote_amount}\n"
         return output
-
-    # https://www.ledger-cli.org/3.0/doc/ledger3.html#Commodities-and-Currencies
-    # > The commodity may be any non-numeric string that does not contain a
-    # > period, comma, forward slash or at-sign. It may appear before or after
-    # > the amount, although it is assumed that symbols appearing before the
-    # > amount refer to currencies, while non-joined symbols appearing after the
-    # > amount refer to commodities.
-
-    # https://www.ledger-cli.org/3.0/doc/ledger3.html#Commoditized-Amounts
-    # > A commoditized amount is an integer amount which has an associated
-    # > commodity. This commodity can appear before or after the amount, and may
-    # > or may not be separated from it by a space. Most characters are allowed
-    # > in a commodity name, except for the following:
-    # > - Any kind of white-space
-    # > - Numerical digits
-    # > - Punctuation: .,;:?!
-    # > - Mathematical and logical operators: -+*/^&|=
-    # > - Bracketing characters: <>[](){}
-    # > - The at symbol: @
-    # > And yet, any of these may appear in a commodity name if it is
-    # > surrounded by double quotes