help: point out need for stringification

mercurial/help/templates.txt

@@ -1,149 +1,150
 Mercurial allows you to customize output of commands through
 templates. You can either pass in a template from the command
 line, via the --template option, or select an existing
 template-style (--style).
 
 You can customize output for any "log-like" command: log,
 outgoing, incoming, tip, parents, heads and glog.
 
 Three styles are packaged with Mercurial: default (the style used
 when no explicit preference is passed), compact and changelog.
 Usage::
 
     $ hg log -r1 --style changelog
 
 A template is a piece of text, with markup to invoke variable
 expansion::
 
     $ hg log -r1 --template "{node}\n"
     b56ce7b07c52de7d5fd79fb89701ea538af65746
 
 Strings in curly braces are called keywords. The availability of
 keywords depends on the exact context of the templater. These
 keywords are usually available for templating a log-like command:
 
 :author: String. The unmodified author of the changeset.
 
 :branches: String. The name of the branch on which the changeset was
     committed. Will be empty if the branch name was default.
 
 :date: Date information. The date when the changeset was committed.
 
 :desc: String. The text of the changeset description.
 
 :diffstat: String. Statistics of changes with the following format:
     "modified files: +added/-removed lines"
 
 :files: List of strings. All files modified, added, or removed by this
     changeset.
 
 :file_adds: List of strings. Files added by this changeset.
 
 :file_copies: List of strings. Files copied in this changeset with
     their sources.
 
 :file_copies_switch: List of strings. Like "file_copies" but displayed
     only if the --copied switch is set.
 
 :file_mods: List of strings. Files modified by this changeset.
 
 :file_dels: List of strings. Files removed by this changeset.
 
 :node: String. The changeset identification hash, as a 40-character
     hexadecimal string.
 
 :parents: List of strings. The parents of the changeset.
 
 :rev: Integer. The repository-local changeset revision number.
 
 :tags: List of strings. Any tags associated with the changeset.
 
 :latesttag: String. Most recent global tag in the ancestors of this
     changeset.
 
 :latesttagdistance: Integer. Longest path to the latest tag.
 
 The "date" keyword does not produce human-readable output. If you
 want to use a date in your output, you can use a filter to process
 it. Filters are functions which return a string based on the input
-variable. You can also use a chain of filters to get the desired
-output::
+variable. Be sure to use the stringify filter first when you're
+applying a string-input filter to a list-like input variable.
+You can also use a chain of filters to get the desired output::
 
    $ hg tip --template "{date|isodate}\n"
    2008-08-21 18:22 +0000
 
 List of filters:
 
 :addbreaks: Any text. Add an XHTML "<br />" tag before the end of
     every line except the last.
 
 :age: Date. Returns a human-readable date/time difference between the
     given date/time and the current date/time.
 
 :basename: Any text. Treats the text as a path, and returns the last
     component of the path after splitting by the path separator
     (ignoring trailing separators). For example, "foo/bar/baz" becomes
     "baz" and "foo/bar//" becomes "bar".
 
 :stripdir: Treat the text as path and strip a directory level, if
     possible. For example, "foo" and "foo/bar" becomes "foo".
 
 :date: Date. Returns a date in a Unix date format, including the
     timezone: "Mon Sep 04 15:13:13 2006 0700".
 
 :domain: Any text. Finds the first string that looks like an email
     address, and extracts just the domain component. Example: ``User
     <[e-mail]>`` becomes ``example.com``.
 
 :email: Any text. Extracts the first string that looks like an email
     address. Example: ``User <[e-mail]>`` becomes
     ``[e-mail]``.
 
 :escape: Any text. Replaces the special XML/XHTML characters "&", "<"
     and ">" with XML entities.
 
 :fill68: Any text. Wraps the text to fit in 68 columns.
 
 :fill76: Any text. Wraps the text to fit in 76 columns.
 
 :firstline: Any text. Returns the first line of text.
 
 :nonempty: Any text. Returns '(none)' if the string is empty.
 
 :hgdate: Date. Returns the date as a pair of numbers: "1157407993
     25200" (Unix timestamp, timezone offset).
 
 :isodate: Date. Returns the date in ISO 8601 format: "2009-08-18 13:00
     +0200".
 
 :isodatesec: Date. Returns the date in ISO 8601 format, including
     seconds: "2009-08-18 13:00:13 +0200". See also the rfc3339date
     filter.
 
 :localdate: Date. Converts a date to local date.
 
 :obfuscate: Any text. Returns the input text rendered as a sequence of
     XML entities.
 
 :person: Any text. Returns the text before an email address.
 
 :rfc822date: Date. Returns a date using the same format used in email
     headers: "Tue, 18 Aug 2009 13:00:13 +0200".
 
 :rfc3339date: Date. Returns a date using the Internet date format
     specified in RFC 3339: "2009-08-18T13:00:13+02:00".
 
 :short: Changeset hash. Returns the short form of a changeset hash,
     i.e. a 12-byte hexadecimal string.
 
 :shortdate: Date. Returns a date like "2006-09-18".
 
 :strip: Any text. Strips all leading and trailing whitespace.
 
 :tabindent: Any text. Returns the text, with every line except the
      first starting with a tab character.
 
 :urlescape: Any text. Escapes all "special" characters. For example,
     "foo bar" becomes "foo%20bar".
 
 :user: Any text. Returns the user portion of an email address.