Swish Cofiguration Options
[account-manager]
account_changes_notify_addresses
List of email addresses that get notified of user changes, ie,
new user, password change and delete user.
authentication_url
force_passwd_change
Forge the user to change password when it's reset.
generated_password_length
Length of the randomly-generated passwords created when resetting the password for an account.
hash_method
htdigest_realm
notify_actions
Comma separated list of actions to notify of.
Available actions 'new', 'change', 'delete'.
password_file
Path to the users file. Leave blank to locate the users file by reading svnserve.conf
password_format
password_store
persistent_sessions
Allow the user to be remembered across sessions without needing to re-authenticate. This is, user checks a "Remember Me" checkbox and, next time he visits the site, he'll be remembered
reset_password
Set to false if there is no email system setup.
[attachment]
max_size
Maximum allowed file size (in bytes) for ticket and wiki
attachments.
render_unsafe_content
Whether attachments should be rendered in the browser, or
only made downloadable.
Pretty much any file may be interpreted as HTML by the browser,
which allows a malicious user to attach a file containing cross-site
scripting attacks.
For public sites where anonymous users can create attachments it is
recommended to leave this option disabled (which is the default).
[browser]
color_scale
Enable colorization of the age column.
This uses the same color scale as the source code annotation:
blue is older, red is newer.
(since 0.11)
downloadable_paths
List of repository paths that can be downloaded.
Leave the option empty if you want to disable all online storage downloads, otherwise
set it to a comma-separated list of authorized paths (those paths are
glob patterns, i.e. "*" can be used as a wild card)
(since 0.10)
hide_properties
Comma-separated list of version control properties to hide from
the repository browser.
(since 0.9)
intermediate_color
(r,g,b) color triple to use for the color corresponding
to the intermediate color, if two linear interpolations are used
for the color scale (see intermediate_point).
If not set, the intermediate color between oldest_color and
newest_color will be used.
(since 0.11)
intermediate_point
If set to a value between 0 and 1 (exclusive), this will be the
point chosen to set the intermediate_color for interpolating
the color value.
(since 0.11)
newest_color
(r,g,b) color triple to use for the color corresponding
to the newest color, for the color scale used in blame or
the browser age column if color_scale is enabled.
(since 0.11)
oldest_color
(r,g,b) color triple to use for the color corresponding
to the oldest color, for the color scale used in blame or
the browser age column if color_scale is enabled.
(since 0.11)
oneliner_properties
Comma-separated list of version control properties to render
as oneliner wiki content in the repository browser.
(since 0.11)
render_unsafe_content
Whether raw files should be rendered in the browser, or only made
downloadable.
Pretty much any file may be interpreted as HTML by the browser,
which allows a malicious user to create a file containing cross-site
scripting attacks.
For open repositories where anyone can check-in a file, it is
recommended to leave this option disabled (which is the default).
wiki_properties
Comma-separated list of version control properties to render
as wiki content in the repository browser.
(since 0.11)
[captchaauth]
type
[captchaauthplus]
dictionary_file
type
[changeset]
max_diff_bytes
Maximum total size in bytes of the modified files (their old size
plus their new size) for which the changeset view will attempt to show
the diffs inlined (since 0.10).
max_diff_files
Maximum number of modified files for which the changeset view will
attempt to show the diffs inlined (since 0.10).
wiki_format_messages
Whether wiki formatting should be applied to changeset messages.
If this option is disabled, changeset messages will be rendered as
pre-formatted text.
[doxygen]
default_documentation
Default documentation project, relative to [doxygen] path.
When no explicit path is given in a documentation request,
this path will be prepended to the request before looking
for documentation files.
default_namespace
Default namespace to search for named objects in.
encoding
Default encoding used by the generated documentation files.
ext
Space separated list of extensions for doxygen managed files.
html_output
Default documentation project suffix, as generated by Doxygen
using the HTML_OUTPUT Doxygen configuration setting.
index
Default index page to pick in the generated documentation.
path
Directory containing doxygen generated files.
source_ext
Space separated list of source files extensions
title
Title to use for the main navigation tab.
wiki_index
Wiki page to use as the default page for the Doxygen main page.
If set, supersedes the [doxygen] index option.
[google.analytics]
admin_logging
Disabling this option will prevent all logged in admins from showing
up on your Google Analytics reports.
authenticated_logging
Disabling this option will prevent all authenticated users from
showing up on your Google Analytics reports.
extensions
Enter any extensions of files you would like to be tracked as a
download. For example to track all MP3s and PDFs enter:
mp3,pdf
Outbound link tracking must be enabled for downloads to be tracked.
google_external_path
This will be the path shown on Google Analytics
regarding external links. Consider the following link:
http://trac.edgewall.org/"
The above link will be shown as for example:
/external/trac.edgewall.org/
This way you will be able to track outgoing links.
Outbound link tracking must be enabled for external links to be
tracked.
outbound_link_tracking
Disabling this option will turn off the tracking of outbound links.
It's recommended not to disable this option unless you're a privacy
advocate (now why would you be using Google Analytics in the first
place?) or it's causing some kind of weird issue.
tracking_domain_name
If you're tracking multiple subdomains with the same Google Analytics
profile, like what's talked about in:
https://www.google.com/support/googleanalytics/bin/answer.py?answer=55524
enter your main domain here. For more info, please visit the previous
link.
uid
Google Analytics' UID.
The UID is needed for Google Analytics to log your website stats.
Your UID can be found by looking in the JavaScript? Google Analytics
gives you to put on your page. Look for your UID in between
var pageTracker = _gat._getTracker("UA-111111-11"); in the javascript.
In this example you would put UA-11111-1 in the UID box.
[header_logo]
alt
Alternative text for the header logo.
height
Height of the header logo image in pixels.
link
URL to link to from header logo.
src
URL of the image to use as header logo.
width
Width of the header logo image in pixels.
[inherit]
plugins_dir
Path of the directory containing additional plugins.
Plugins in that directory are loaded in addition to those in the
directory of the environment plugins, with this one taking
precedence.
(since 0.11)
templates_dir
Path to the shared templates directory.
Templates in that directory are loaded in addition to those in the
environments templates directory, but the latter take precedence.
(since 0.11)
[iniadmin]
excludes
Excludes this options.
Comma separated list as section:name.
passwords
Show input-type as password instead of text.
Comma separated list as section:name.
[logging]
log_file
If log_type is file, this should be a path to the log-file.
log_format
Custom logging format.
If nothing is set, the following will be used:
Trac[$(module)s] $(levelname)s: $(message)s
In addition to regular key names supported by the Python logger library
library (see http://docs.python.org/lib/node422.html), one could use:
- $(path)s the path for the current environment
- $(basename)s the last path component of the current environment
- $(project)s the project name
Note the usage of $(...)s instead of %(...)s as the latter form
would be interpreted by the ConfigParser? itself.
Example:
($(thread)d) Trac[$(basename)s:$(module)s] $(levelname)s: $(message)s
(since 0.10.5)
log_level
Level of verbosity in log.
Should be one of (CRITICAL, ERROR, WARN, INFO, DEBUG).
log_type
Logging facility to use.
Should be one of (none, file, stderr, syslog, winlog).
[milestone]
stats_provider
Name of the component implementing ITicketGroupStatsProvider,
which is used to collect statistics on groups of tickets for display
in the milestone views.
[mimeviewer]
enscript_modes
List of additional MIME types known by Enscript.
For each, a tuple mimetype:mode:quality has to be
specified, where mimetype is the MIME type,
mode is the corresponding Enscript mode to be used
for the conversion and quality is the quality ratio
associated to this conversion.
That can also be used to override the default
quality ratio used by the Enscript render, which is 2
(since 0.10).
enscript_path
Path to the Enscript executable.
max_preview_size
Maximum file size for HTML preview. (since 0.9)
mime_map
List of additional MIME types and keyword mappings.
Mappings are comma-separated, and for each MIME type,
there's a colon (":") separated list of associated keywords
or file extensions. (since 0.10)
php_path
Path to the PHP executable (since 0.9).
pygments_default_style
The default style to use for Pygments syntax highlighting.
pygments_modes
List of additional MIME types known by Pygments.
For each, a tuple mimetype:mode:quality has to be
specified, where mimetype is the MIME type,
mode is the corresponding Pygments mode to be used
for the conversion and quality is the quality ratio
associated to this conversion. That can also be used
to override the default quality ratio used by the
Pygments render.
tab_width
Displayed tab width in file preview. (since 0.9)
treat_as_binary
Comma-separated list of MIME types that should be treated as
binary data. (since 0.11.5)
[notification]
admit_domains
Comma-separated list of domains that should be considered as
valid for email addresses (such as localdomain)
always_notify_owner
Always send notifications to the ticket owner (since 0.9).
always_notify_reporter
Always send notifications to any address in the reporter
field.
always_notify_updater
Always send notifications to the person who causes the ticket
property change and to any previous updater of that ticket.
ignore_domains
Comma-separated list of domains that should not be considered
part of email addresses (for usernames with Kerberos domains)
mime_encoding
Specifies the MIME encoding scheme for emails.
Valid options are 'base64' for Base64 encoding, 'qp' for
Quoted-Printable, and 'none' for no encoding, in which case mails will
be sent as 7bit if the content is all ASCII, or 8bit otherwise.
(since 0.10)
smtp_always_bcc
Email address(es) to always send notifications to,
addresses do not appear publicly (Bcc:). (since 0.10).
smtp_always_cc
Email address(es) to always send notifications to,
addresses can be seen by all recipients (Cc:).
smtp_default_domain
Default host/domain to append to address that do not specify one
smtp_enabled
Enable SMTP (email) notification.
smtp_from
Sender address to use in notification emails.
smtp_from_name
Sender name to use in notification emails.
smtp_password
Password for SMTP server. (since 0.9).
smtp_port
SMTP server port to use for email notification.
smtp_replyto
Reply-To address to use in notification emails.
smtp_server
SMTP server hostname to use for email notifications.
smtp_subject_prefix
Text to prepend to subject line of notification emails.
If the setting is not defined, then the [$project_name] prefix.
If no prefix is desired, then specifying an empty option
will disable it. (since 0.10.1).
smtp_user
Username for SMTP server. (since 0.9).
ticket_subject_template
A Genshi text template snippet used to get the notification subject.
By default, the subject template is $prefix #$ticket.id: $summary.
$prefix being the value of the smtp_subject_prefix option.
(since 0.11)
use_public_cc
Recipients can see email addresses of other CC'ed recipients.
If this option is disabled (the default), recipients are put on BCC
(since 0.10).
use_short_addr
Permit email address without a host/domain (i.e. username only)
The SMTP server should accept those addresses, and either append
a FQDN or use local delivery (since 0.10).
use_tls
Use SSL/TLS to send notifications (since 0.10).
[openid]
absolute_trust_root
Whether we should use absolute trust root or by project.
black_list
Comma separated list of denied OpenId? addresses.
check_list
JSON service for openid check.
check_list_key
Key for openid Service.
check_list_username
Username for openid Service.
combined_username
Username will be written as username_in_remote_system<openid_url>.
custom_provider_image
Custom OpenId? provider image.
custom_provider_label
Custom OpenId? provider label.
custom_provider_name
Custom OpenId? provider name.
custom_provider_url
Custom OpenId? provider URL. E.g.: http://claimid.com/{username}
default_openid
Default OpenID provider for directed identity.
pape_method
Default PAPE method to request from OpenID provider.
signup
Signup link
sreg_required
Whether SREG data should be required or optional.
strip_protocol
Instead of using username beginning with http:// or https:// you can strip the beginning.
strip_trailing_slash
In case your OpenID is some sub-domain address OpenId? library adds trailing slash. This option strips it.
timeout
Specify if expiration time should act as timeout.
whatis
What is OpenId? link.
white_list
Comma separated list of allowed OpenId? addresses.
[project]
admin
E-Mail address of the project's administrator.
admin_trac_url
Base URL of a Trac instance where errors in this Trac should be
reported.
This can be an absolute or relative URL, or '.' to reference this
Trac instance. An empty value will disable the reporting buttons.
(since 0.11.3)
descr
Short description of the project.
footer
Page footer text (right-aligned).
icon
URL of the icon of the project.
name
Name of the project.
url
URL of the main project web site, usually the website in which
the base_url resides.
[query]
default_anonymous_query
The default query for anonymous users. The query is either
in query language syntax, or a URL query
string starting with ? as used in query:
Trac links.
(since 0.11.2)
default_query
The default query for authenticated users. The query is either
in query language syntax, or a URL query
string starting with ? as used in query:
Trac links.
(since 0.11.2)
items_per_page
Number of tickets displayed per page in ticket queries,
by default (since 0.11)
[report]
items_per_page
Number of tickets displayed per page in ticket reports,
by default (since 0.11)
items_per_page_rss
Number of tickets displayed in the rss feeds for reports
(since 0.11)
[revisionlog]
default_log_limit
Default value for the limit argument in the TracRevisionLog
(since 0.11).
[roadmap]
stats_provider
Name of the component implementing ITicketGroupStatsProvider,
which is used to collect statistics on groups of tickets for display
in the roadmap views.
[search]
min_query_length
Minimum length of query string allowed when performing a search.
[spam-filter]
akismet_api_key
Wordpress key required to use the Akismet API.
akismet_api_url
URL of the Akismet service.
akismet_karma
By how many points an Akismet reject impacts the overall karma of
a submission.
attachment_karma
The karma given to attachments.
attachment_sample_size
The number of bytes from an attachment to pass through the spam
filters.
authenticated_karma
The karma given to authenticated users, in case
trust_authenticated is false.
badcontent_file
Local file to be loaded to get BadContent?. Can be used in
addition to BadContent? wiki page.
bayes_karma
By what factor Bayesian spam probability score affects the overall
karma of a submission.
bayes_min_training
The minimum number of submissions in the training database required
for the filter to start impacting the karma of submissions.
captcha
CAPTCHA method to use for verifying humans.
captcha_expression_ceiling
Maximum value of individual terms in numeric CAPTCHA
expression.
captcha_expression_terms
Number of terms in numeric CAPTCHA expression.
captcha_image_alphabet
Alphabet to choose image CAPTCHA challenge from.
captcha_image_font_size
Font size to use in image CAPTCHA.
captcha_image_fonts
Set of fonts to choose from when generating image CAPTCHA.
captcha_image_letters
Number of letters to use in image CAPTCHA challenge.
captcha_karma
By how many points a successful CAPTCHA response increases the
overall score.
captcha_karma_lifetime
Time in seconds that a successful CAPTCHA response increases
karma.
captcha_recaptcha_private_key
Private key for recaptcha usage..
captcha_recaptcha_public_key
Public key for recaptcha usage..
extlinks_allowed_domains
List of domains that should be allowed in external links
extlinks_karma
By how many points too many external links in a submission impact
the overall score.
httpbl_api_key
Http:BL API key required for use.
httpbl_spammer_karma
By how many points listing as "comment spammer" impacts the
overall karma of a submission.
ip_blacklist_karma
By how many points blacklisting by a single server impacts the
overall karma of a submission.
ip_blacklist_servers
Servers used for IP blacklisting.
ip_throttle_karma
By how many points exceeding the configured maximum number of posts
per hour impacts the overall score.
is_forwarded
Interpret X-Forwarded-For header for IP checks.
logging_enabled
Whether all content submissions and spam filtering activity should
be logged to the database.
max_external_links
The maximum number of external links allowed in a submission until
that submission gets negative karma.
max_posts_by_ip
The maximum allowed number of submissions per hour form a single IP
address. If this limit is exceeded, subsequent permissions get negative
karma.
min_karma
The minimum score required for a submission to be allowed.
purge_age
The number of days after which log entries should be purged.
regex_karma
By how many points a match with a pattern on the BadContent? page
impacts the overall karma of a submission.
reject_handler
The handler used to reject content.
session_karma
By how many points an existing and configured session improves the
overall karma of the submission. A third of the points is granted for
having an existing session at all, the other two thirds are granted
when the user has his name and/or email address set in the session,
respectively.
show_blacklisted
Show the matched bad content patterns in rejection message.
trust_authenticated
Whether content submissions by authenticated users should be trusted
without checking for potential spam or other abuse.
typepad_api_key
TypePad? key required to use the TypePad? AntiSpam? API.
typepad_api_url
URL of the TypePad? service.
typepad_karma
By how many points an TypePad? reject impacts the overall karma of
a submission.
[svn]
branches
Comma separated list of paths categorized as branches.
If a path ends with '*', then all the directory entries found below
that path will be included.
Example: /trunk, /branches/*, /projectAlpha/trunk, /sandbox/*
tags
Comma separated list of paths categorized as tags.
If a path ends with '*', then all the directory entries found below
that path will be included.
Example: /tags/*, /projectAlpha/tags/A-1.0, /projectAlpha/tags/A-v1.1
[ticket]
default_cc
Default cc: list for newly created tickets.
default_component
Default component for newly created tickets.
default_description
Default description for newly created tickets.
default_keywords
Default keywords for newly created tickets.
default_milestone
Default milestone for newly created tickets.
default_owner
Default owner for newly created tickets.
default_priority
Default priority for newly created tickets.
default_resolution
Default resolution for resolving (closing) tickets
(since 0.11).
default_severity
Default severity for newly created tickets.
default_summary
Default summary (title) for newly created tickets.
default_type
Default type for newly created tickets (since 0.9).
default_version
Default version for newly created tickets.
max_comment_size
Don't accept tickets with a too big comment.
(since 0.11.2)
max_description_size
Don't accept tickets with a too big description.
(since 0.11).
preserve_newlines
Whether Wiki formatter should respect the new lines present
in the Wiki text.
If set to 'default', this is equivalent to 'yes' for new environments
but keeps the old behavior for upgraded environments (i.e. 'no').
(since 0.11).
restrict_owner
Make the owner field of tickets use a drop-down menu.
Be sure to understand the performance implications before activating
this option. See
Assign-to as Drop-Down List
(since 0.9).
workflow
Ordered list of workflow controllers to use for ticket actions
(since 0.11).
[timeline]
abbreviated_messages
Whether wiki-formatted event messages should be truncated or not.
This only affects the default rendering, and can be overriden by
specific event providers, see their own documentation.
(Since 0.11)
changeset_collapse_events
Whether consecutive changesets from the same author having
exactly the same message should be presented as one event.
That event will link to the range of changesets in the log view.
(since 0.11)
changeset_long_messages
Whether wiki-formatted changeset messages should be multiline or not.
If this option is not specified or is false and wiki_format_messages
is set to true, changeset messages will be single line only, losing
some formatting (bullet points, etc).
changeset_show_files
Number of files to show (-1 for unlimited, 0 to disable).
This can also be location, for showing the common prefix for the
changed files. (since 0.11).
default_daysback
Default number of days displayed in the Timeline, in days.
(since 0.9.)
max_daysback
Maximum number of days (-1 for unlimited) displayable in the
Timeline. (since 0.11)
newticket_formatter
Which formatter flavor (e.g. 'html' or 'oneliner') should be
used when presenting the description for new tickets.
If 'oneliner', the [timeline] abbreviated_messages option applies.
(since 0.11).
ticket_show_details
Enable the display of all ticket changes in the timeline, not only
open / close operations (since 0.9).
[trac]
authz_file
Path to Subversion
authorization (authz) file
authz_module_name
The module prefix used in the authz_file.
auto_reload
Automatically reload template files after modification.
backup_dir
Database backup location
base_url
Reference URL for the Trac deployment.
This is the base URL that will be used when producing documents that
will be used outside of the web browsing context, like for example
when inserting URLs pointing to Trac resources in notification
e-mails.
check_auth_ip
Whether the IP address of the user should be checked for
authentication (since 0.9).
check_auth_ip_mask
What mask should be applied to user address.
database
Database connection
string for this
project
debug_sql
Show the SQL queries in the Trac log, at DEBUG level.
(Since 0.11.5)
default_charset
Charset to be used when in doubt.
default_handler
Name of the component that handles requests to the base URL.
Options include TimelineModule, RoadmapModule, BrowserModule,
QueryModule, ReportModule, TicketModule and WikiModule. The
default is WikiModule. (since 0.9)
default_timezone
The default timezone to use
expires
Specify how fast authentication expires.
htdocs_location
Base URL of the core static resources.
ignore_auth_case
Whether login names should be converted to lower case
(since 0.9).
mainnav
Order of the items to display in the mainnav navigation bar,
listed by IDs. See also TracNavigation.
metanav
Order of the items to display in the metanav navigation bar,
listed by IDs. See also TracNavigation.
mysqldump_path
Location of mysqldump for MySQL database backups
never_obfuscate_mailto
Never obfuscate mailto: links explicitly written in the wiki,
even if show_email_addresses is false or the user has not the
EMAIL_VIEW permission (since 0.11.6).
permission_policies
List of components implementing IPermissionPolicy, in the order in
which they will be applied. These components manage fine-grained access
control to Trac resources.
Defaults to the DefaultPermissionPolicy? (pre-0.11 behavior) and
LegacyAttachmentPolicy? (map ATTACHMENT_* permissions to realm specific
ones)
permission_store
Name of the component implementing IPermissionStore, which is used
for managing user and group permissions.
pg_dump_path
Location of pg_dump for Postgres database backups
repository_dir
Path to local repository. This can also be a relative path
(since 0.11).
repository_type
Repository connector type. (since 0.10)
request_filters
Ordered list of filters to apply to all requests
(since 0.10).
secure_cookies
Restrict cookies to HTTPS connections.
When true, set the secure flag on all cookies so that they are
only sent to the server on HTTPS connections. Use this if your Trac
instance is only accessible through HTTPS. (since 0.11.2)
show_email_addresses
Show email addresses instead of usernames. If false, we obfuscate
email addresses (since 0.11).
show_ip_addresses
Show IP addresses for resource edits (e.g. wiki).
(since 0.11.3).
timeout
Timeout value for database connection, in seconds.
Use '0' to specify no timeout. (Since 0.11)
use_base_url_for_redirect
Optionally use [trac] base_url for redirects.
In some configurations, usually involving running Trac behind a HTTP
proxy, Trac can't automatically reconstruct the URL that is used to
access it. You may need to use this option to force Trac to use the
base_url setting also for redirects. This introduces the obvious
limitation that this environment will only be usable when accessible
from that URL, as redirects are frequently used. (since 0.10.5)
[wiki]
ignore_missing_pages
Enable/disable highlighting CamelCase links to missing pages
(since 0.9).
max_size
Maximum allowed wiki page size in bytes. (since 0.11.2)
render_unsafe_content
Enable/disable the use of unsafe HTML tags such as <script> or
<embed> with the HTML WikiProcessor
(since 0.10.4).
For public sites where anonymous users can edit the wiki it is
recommended to leave this option disabled (which is the default).
split_page_names
Enable/disable splitting the WikiPageNames with space characters
(since 0.10).
[components]
This section is used to enable or disable components provided by plugins, as well as by Trac itself. The component to enable/disable is specified via the name of the option. Whether its enabled is determined by the option value; setting the value to enabled or on will enable the component, any other value (typically disabled or off) will disable the component.
The option name is either the fully qualified name of the components or the module/package prefix of the component. The former enables/disables a specific component, while the latter enables/disables any component in the specified package/module.
Consider the following configuration snippet:
[components] trac.ticket.report.ReportModule = disabled webadmin.* = enabled
The first option tells Trac to disable the report module. The second option instructs Trac to enable all components in the webadmin package. Note that the trailing wildcard is required for module/package matching.
See the Plugins page on About Trac to get the list of active components (requires CONFIG_VIEW permissions.)
See also: TracPlugins
[ticket-custom]
In this section, you can define additional fields for tickets. See TracTicketsCustomFields for more details.
[ticket-workflow]
(since 0.11)
The workflow for tickets is controlled by plugins. By default, there's only a ConfigurableTicketWorkflow component in charge. That component allows the workflow to be configured via this section in the trac.ini file. See TracWorkflow for more details.
[milestone-groups]
(since 0.11)
As the workflow for tickets is now configurable, there can be many ticket states, and simply displaying closed tickets vs. all the others is maybe not appropriate in all cases. This section enables one to easily create groups of states that will be shown in different colors in the milestone progress bar.
Example configuration (which is also the default):
closed = closed closed.order = 0 # sequence number in the progress bar closed.query_args = group=resolution # optional extra param for the query closed.overall_completion = true # count for overall completion active = * # one catch-all group is allowed active.order = 1 active.css_class = open # CSS class for this interval active.label = in progress # Displayed label for this group
The definition consists in a comma-separated list of accepted status. Also, '*' means any status and could be used to associate all remaining states to one catch-all group.
The CSS class can be one of: new (yellow), open (no color) or closed (green). New styles can easily be added using the following selector: table.progress td.<class>
[svn:externals]
(since 0.11)
The TracBrowser for Subversion can interpret the svn:externals property of folders out of the box. However, if those externals are not using the http: protocol, or if a link to a different repository browser (such another Trac or ViewVC) is desired, then Trac needs to be able to map an external prefix to this other URL.
This mapping is done in the [svn:externals] section of the TracIni