This is the manual for the
url Emacs Lisp library.
Copyright © 1993–1999, 2002, 2004–2018 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License”.
(a) The FSF's Back-Cover Text is: “You have the freedom to copy and modify this GNU manual.”
|URI Parsing||Parsing (and unparsing) URIs.|
|Retrieving URLs||How to use this package to retrieve a URL.|
|Supported URL Types||Descriptions of URL types currently supported.|
|General Facilities||URLs can be cached, accessed via a gateway and tracked in a history list.|
|Customization||Variables you can alter.|
|GNU Free Documentation License||The license for this documentation.|
A Uniform Resource Identifier (URI) is a specially-formatted name, such as an Internet address, that identifies some name or resource. The format of URIs is described in RFC 3986, which updates and replaces the earlier RFCs 2732, 2396, 1808, and 1738. A Uniform Resource Locator (URL) is an older but still-common term, which basically refers to a URI corresponding to a resource that can be accessed (usually over a network) in a specific way.
Here are some examples of URIs (taken from RFC 3986):
ftp://ftp.is.co.za/rfc/rfc1808.txt http://www.ietf.org/rfc/rfc2396.txt ldap://[2001:db8::7]/c=GB?objectClass?one mailto:John.Doe@example.com news:comp.infosystems.www.servers.unix tel:+1-816-555-1212 telnet://192.0.2.16:80/ urn:oasis:names:specification:docbook:dtd:xml:4.1.2
This manual describes the
url library, an Emacs Lisp library
for parsing URIs and retrieving the resources to which they refer.
(The library is so-named for historical reasons; nowadays, the “URI”
terminology is regarded as the more general one, and “URL” is
technically obsolete despite its widespread vernacular usage.)
2 URI Parsing
A URI consists of several components, each having a different meaning. For example, the URI
specifies the scheme component ‘https’, the hostname component ‘www.gnu.org’, and the path component ‘/software/emacs/’.
The format of URIs is specified by RFC 3986. The
provides the Lisp function
url-generic-parse-url, a (mostly)
standard-compliant URI parser, as well as function
url-recreate-url, which converts a parsed URI back into a URI
This function returns a parsed version of the string uri-string.
The return value of
url-generic-parse-url, and the argument
url-recreate-url, is a parsed URI: a CL
structure whose slots hold the various components of the URI.
See the CL Manual, for
details about CL structures. Most of the other functions in the
url library act on parsed URIs.
2.1 Parsed URI structures
Each parsed URI structure contains the following slots:
- The URI scheme (a string, e.g.,
http). See Supported URL Types, for a list of schemes that the
urllibrary knows how to process. This slot can also be
nil, if the URI is not fully specified.
- The user name (a string), or
- The user password (a string), or
nil. The use of this URI component is strongly discouraged; nowadays, passwords are transmitted by other means, not as part of a URI.
- The host name (a string), or
nil. If present, this is typically a domain name or IP address.
- The port number (an integer), or
nil. Omitting this component usually means to use the “standard” port associated with the URI scheme.
- The combination of the “path” and “query” components of the URI (a
nil. If the query component is present, it is the substring following the first ‘?’ character, and the path component is the substring before the ‘?’. The meaning of these components is scheme-dependent; they do not necessarily refer to a file on a disk.
- The fragment component (a string), or
nil. The fragment component specifies a “secondary resource”, such as a section of a webpage.
- This is
tif the URI is fully specified, i.e., the hierarchical components of the URI (the hostname and/or username and/or password) are preceded by ‘//’.
These slots have accessors named
part is the slot name. For example, the accessor for the
host slot is the function
accessor returns the default port for the URI scheme if the parsed
URI's port slot is
The slots can be set using
setf. For example:
(setf (url-port url) 80)
2.2 URI Encoding
Strictly speaking, RFC 3986 compatible URIs may only consist of ASCII characters; non-ASCII characters are represented by converting them to UTF-8 byte sequences, and performing percent encoding on the bytes. For example, the o-umlaut character is converted to the UTF-8 byte sequence ‘\xD3\xA7’, then percent encoded to ‘%D3%A7’. (Certain “reserved” ASCII characters must also be percent encoded when they appear in URI components.)
url-encode-url can be used to convert a URI
string containing arbitrary characters to one that is properly
percent-encoded in accordance with RFC 3986.
This function return a properly URI-encoded version of url-string. It also performs URI normalization, e.g., converting the scheme component to lowercase if it was previously uppercase.
To convert between a string containing arbitrary characters and a
percent-encoded all-ASCII string, use the functions
This function performs percent-encoding on string, and returns the result.
If string is multibyte, it is first converted to a UTF-8 byte string. Each byte corresponding to an allowed character is left as-is, while all other bytes are converted to a three-character sequence: ‘%’ followed by two upper-case hex digits.
The allowed characters are specified by allowed-chars. If this argument is
nil, the allowed characters are those specified as unreserved characters by RFC 3986 (see the variable
url-unreserved-chars). Otherwise, allowed-chars should be a vector whose n-th element is non-
nilif character n is allowed.
This function replaces percent-encoding sequences in string with their character equivalents, and returns the resulting string.
If allow-newlines is non-
nil, it allows the decoding of carriage returns and line feeds, which are normally forbidden in URIs.
3 Retrieving URLs
url library defines the following three functions for
retrieving the data specified by a URL. The actual retrieval protocol
depends on the URL's URI scheme, and is performed by lower-level
scheme-specific functions. (Those lower-level functions are not
documented here, and generally should not be called directly.)
In each of these functions, the url argument can be either a
string or a parsed URL structure. If it is a string, that string is
url-encode-url before using it, to ensure that
it is properly URI-encoded (see URI Encoding).
This function synchronously retrieves the data specified by url, and returns a buffer containing the data. The return value is
nilif there is no data associated with the URL (as is the case for
If the optional argument silent is non-
nil, progress messages are suppressed. If the optional argument no-cookies is non-
nil, cookies are not stored or sent. If the optional argument timeout is non-
nil, it should be a number that says (in seconds) how long to wait for a response before giving up.
This function retrieves url asynchronously, calling the function callback when the object has been completely retrieved. The return value is the buffer into which the data will be inserted, or
nilif the process has already completed.
The callback function is called this way:(apply callback status cbargs)
where status is a plist representing what happened during the retrieval, with most recent events first, or an empty list if no events have occurred. Each pair in the plist is one of:
- This means that the request was redirected to the URL redirected-to.
- This means that an error occurred. If so desired, the error can be signaled with
When the callback function is called, the current buffer is the one containing the retrieved data (if any). The buffer also contains any MIME headers associated with the data retrieval.
If the optional argument silent is non-
nil, progress messages are suppressed. If the optional argument no-cookies is non-
nil, cookies are not stored or sent.
This function acts like
url-retrieve, but with limits on the number of concurrently-running network processes. The option
url-queue-parallel-processescontrols the number of concurrent processes, and the option
url-queue-timeoutsets a timeout in seconds.
To use this function, you must
The value of this option is an integer specifying the maximum number of concurrent
url-queue-retrievenetwork processes. If the number of
url-queue-retrievecalls is larger than this number, later ones are queued until earlier ones are finished.
The value of this option is a number specifying the maximum lifetime of a
url-queue-retrievenetwork process, once it is started. If a process is not finished by then, it is killed and removed from the queue.
4 Supported URL Types
This chapter describes functions and variables affecting URL retrieval for specific schemes.
http scheme refers to the Hypertext Transfer Protocol. The
url library supports HTTP version 1.1, specified in RFC 2616.
Its default port is 80.
https scheme is a secure version of
transmission via SSL. It is defined in RFC 2069, and its default port
is 443. When using
url library performs SSL
encryption via the
ssl library, by forcing the
gateway method to be used. See Gateways in general.
If this option is non-
nil(the default), the
urllibrary honors the HTTP ‘Refresh’ header, which is used by servers to direct clients to reload documents from the same URL or a different one. If the value is
nil, the ‘Refresh’ header is ignored; any other value means to ask the user on each request.
This command creates a *url cookies* buffer listing the current cookies, if there are any. You can remove a cookie using the C-k (
This function takes a regular expression as its parameters and deletes all cookies from that domain. If regexp is
nil, delete all cookies.
The file in which cookies are stored, defaulting to cookies in the directory specified by
Specifies whether confirmation is required to accept cookies.
Specifies whether to put all cookies for the server on one line in the HTTP request to satisfy broken servers like http://www.hotmail.com.
A list of regular expressions matching URLs from which to accept cookies always.
A list of regular expressions matching URLs from which to reject cookies always.
The number of seconds between automatic saves of cookies to disk. Default is one hour.
4.1.2 Language and Encoding Preferences
HTTP allows clients to express preferences for the language and encoding of documents which servers may honor. For each of these variables, the value is a string; it can specify a single choice, or it can be a comma-separated list.
Normally, this list is ordered by descending preference. However, each
element can be followed by ‘;q=priority’ to specify its
preference level, a decimal number from 0 to 1; e.g., for
"de, en-gb;q=0.8, en;q=0.7". An element that has no ‘;q’ specification has
preference level 1.
HTTP allows specifying a series of MIME charsets which indicate your preferred character set encodings, e.g., Latin-9 or Big5, and these can be weighted. The default series is generated automatically from the associated MIME types of all defined coding systems, sorted by the coding system priority specified in Emacs. See Recognizing Coding Systems.
The string can be
"*"to get the first available language (as opposed to the default).
4.1.3 HTTP URL Options
HTTP supports an ‘OPTIONS’ method describing things supported by the URL.
Returns a property list describing options available for URL. The property list members are:
- A list of symbols specifying what HTTP methods the resource supports.
- A list of numbers specifying what DAV protocol/schema versions are supported.
- A list of supported DASL search types supported (string form).
- A list of the units available for use in partial document fetches.
- The Platform For Privacy Protection description for the resource. Currently this is just the raw header contents.
4.1.4 Dealing with HTTP documents
HTTP URLs are retrieved into a buffer containing the HTTP headers followed by the body. Since the headers are quasi-MIME, they may be processed using the MIME library. See Emacs MIME.
4.2 file and ftp
If the URL specifies a local file, it is retrieved by reading the file contents in the usual way. If it specifies a remote file, it is retrieved using either the Tramp or the Ange-FTP package. See Remote Files.
When retrieving a compressed file, it is automatically uncompressed
if it has the file suffix .z, .gz, .Z,
.bz2, or .xz. (The list of supported suffixes is
hard-coded, and cannot be altered by customizing
This option specifies the filename to look for when a
ftpURL specifies a directory. The default is index.html. If this file exists and is readable, it is viewed. Otherwise, Emacs visits the directory using Dired.
and are retrieved by invoking
Info-goto-node with argument
‘(file)node’. If ‘#node’ is omitted, the
‘Top’ node is opened.
mailto URL specifies an email message to be sent to a given
email address. For example, ‘mailto:firstname.lastname@example.org’ specifies
sending a message to ‘email@example.com’. The “retrieval method”
for such URLs is to open a mail composition buffer in which the
appropriate content (e.g., the recipient address) has been filled in.
As defined in RFC 6068, a
mailto URL can have the form
where an arbitrary number of headers can be added. If the
header is ‘body’, then contents is put in the message
body; otherwise, a header header field is created with
contents as its contents. Note that the
url library does
not perform any checking of header or contents, so you
should check them before sending the message.
The value of this variable is the function called whenever url needs to send mail. This should normally be left its default, which is the standard mail-composition command
compose-mail. See Sending Mail.
If the document containing the
mailto URL itself possessed a
known URL, Emacs automatically inserts an ‘X-Url-From’ header
field into the mail buffer, specifying that URL.
snews schemes, defined in RFC
1738, are used for reading Usenet newsgroups. For compatibility with
non-standard-compliant news clients, the
url library allows
host and port fields to be included in
news URLs, even though
they are properly only allowed for
nntp URLs have the following form:
- Retrieves a list of messages in newsgroup;
- Retrieves the message with the given message-id;
- Retrieves a list of all available newsgroups;
- Similar to the ‘news’ versions.
The default port for
news) is 119. The
difference between an
nntp URL and a
news URL is that an
nttp URL may specify an article by its number. The
‘snews’ scheme is the same as ‘nntp’, except that it is
tunneled through SSL and has default port 563.
These URLs are retrieved via the Gnus package.
This variable specifies the default news server from which to fetch news, if no server was specified in the URL. The default value,
nil, means to use the server specified by the standard environment variable ‘NNTPSERVER’, or ‘news’ if that environment variable is unset.
4.6 rlogin, telnet and tn3270
but the password component is ignored. By default, the
telnet scheme is handled via Tramp (see Tramp).
To handle rlogin, telnet and tn3270 URLs, a
tn3270 (the program names and arguments are
hardcoded) session is run in a
Well-known ports are used if the URL does not specify a port.
irc scheme is defined in the Internet Draft at
was never approved as an RFC). Such URLs have the form
and are retrieved by opening an IRC session using the
function specified by
The value of this option is a function, which is called to open an IRC connection for
ircURLs. This function must take five arguments, host, port, channel, user and password. The channel argument specifies the channel to join immediately, and may be
The default is
url-irc-rcirc, which uses the Rcirc package. Other options are
url-irc-erc(which uses ERC) and
url-irc-zenirc(which uses ZenIRC).
media-type is a MIME ‘Content-Type’ string, possibly including parameters. It defaults to ‘text/plain;charset=US-ASCII’. The ‘text/plain’ can be omitted but the charset parameter supplied. If ‘;base64’ is present, the data are base64-encoded.
nfs://user:password@host:port/file%’ sequences are recognized:
- The hostname of the NFS server;
- The port number of the NFS server;
- The username to use to authenticate;
- The password to use to authenticate;
- The filename on the remote server;
- A literal ‘%’.
Each can be used any number of times.
and are retrieved by passing page-spec to the Lisp function
4.12 URL Types Supported via Tramp
Some additional URL types are supported by passing them to Tramp
(see The Tramp Manual). These
protocols are listed in the
url-tramp-protocols variable, which
you can customize. The default value includes the following
- The file transfer protocol. See file/ftp.
- The secure shell protocol. See Inline methods.
- The secure file copy protocol. See External methods.
- The remote sync protocol.
- The telnet protocol.
5 General Facilities
5.1 Disk Caching
The disk cache stores retrieved documents locally, whence they can be retrieved more quickly. When requesting a URL that is in the cache, the library checks to see if the page has changed since it was last retrieved from the remote machine. If not, the local copy is used, saving the transmission over the network. Currently the cache isn't cleared automatically.
Setting this variable non-
nilcauses documents to be cached automatically.
This variable specifies the directory to store the cache files. It defaults to sub-directory cache of
The cache relies on a scheme for mapping URLs to files in the cache. This variable names a function which sets the type of cache to use. It takes a URL as argument and returns the absolute file name of the corresponding cache file. The two supplied possibilities are
(url-cache-create-filename-using-md5 "http://www.example.com/foo/bar") ⇒ "/home/fx/.url/cache/fx/http/com/example/www/b8a35774ad20db71c7c3409a5410e74f"
Creates a cache file name from url more obviously connected to url than for
url-cache-create-filename-using-md5, but more likely to conflict with other files.(url-cache-create-filename-human-readable "http://www.example.com/foo/bar") ⇒ "/home/fx/.url/cache/fx/http/com/example/www/foo/bar"
This function returns non-
nilif a cache entry has expired (or is absent). The arguments are a URL and optional expiration delay in seconds (default url-cache-expire-time).
This variable is the default number of seconds to use for the expire-time argument of the function
This function takes a URL as its argument and returns a buffer containing the data cached for that URL.
5.2 Proxies and Gatewaying
Proxy servers are commonly used to provide gateways through firewalls
or as caches serving some more-or-less local network. Each protocol
(HTTP, FTP, etc.) can have a different gateway server. Proxying is
conventionally configured commonly amongst different programs through
environment variables of the form protocol
protocol is one of the supported network protocols (
ftp etc.). The library recognizes such variables in either
upper or lower case. Their values are of one of the forms:
- A full URL;
- Simply a host name.
NO_PROXY environment variable specifies URLs that should be
excluded from proxying (on servers that should be contacted directly).
This should be a comma-separated list of hostnames, domain names, or a
mixture of both. Asterisks can be used as wildcards, but other
clients may not support that. Domain names may be indicated by a
leading dot. For example:
says to contact all machines in the ‘aventail.com’ and
‘seanet.com’ domains directly, as well as the machine named
NO_PROXY isn't defined,
no_proxy are also tried, in that order.
Proxies may also be specified directly in Lisp.
This variable is an alist of URL schemes and proxy servers that gateway them. The items are of the form
), says that the URL scheme is gatewayed through portnumber on the specified host. An exception is the pseudo scheme
"no_proxy", which is paired with a regexp matching host names not to be proxied. This variable is initialized from the environment as above.(setq url-proxy-services '(("http" . "proxy.aventail.com:80") ("no_proxy" . "^.*\\(aventail\\|seanet\\)\\.com")))
5.3 Gateways in General
The library provides a general gateway layer through which all
networking passes. It can both control access to the network and
provide access through gateways in firewalls. This may make direct
connections in some cases and pass through some sort of gateway in
others.1 The library's basic function responsible for
making connections is
This is a regular expression that matches local hosts that do not require the use of a gateway. If
nil, all connections are made through the gateway.
This variable controls which gateway method is used. It may be useful to bind it temporarily in some applications. It has values taken from a list of symbols. Possible values are:
- Use this method if you must first telnet and log into a gateway host, and then run telnet from that host to connect to outside machines.
- This method is identical to
telnet, but uses rlogin to log into the remote machine without having to send the username and password over the wire every time.
- Use if the firewall has a socks gateway running on it. The socks v5 protocol is defined in RFC 1928.
- This method uses Emacs's builtin networking directly. This is the default. It can be used only if there is no firewall blocking access.
The following variables control the gateway methods.
The gateway host to telnet to. Once logged in there, you then telnet out to the hosts you want to connect to.
This should be a list of parameters to pass to the telnet program.
This is a regular expression that matches the password prompt when logging in.
This is a regular expression that matches the username prompt when logging in.
This is a regular expression that matches the shell prompt.
This is a regular expression that matches the shell prompt.
This specifies the default server, it takes the form
)where version can be either 4 or 5.
If this is
nilthen you will be asked for the password, otherwise it will be used as the password for authenticating you to the socks server.
This is the username to use when authenticating yourself to the socks server. By default this is your login name.
This controls how long, in seconds, to wait for responses from the socks server; it is 5 by default.
5.3.1 Suppressing Network Connections
In some circumstances it is desirable to suppress making network connections. A typical case is when rendering HTML in a mail user agent, when external URLs should not be activated, particularly to avoid “bugs” which “call home” by fetch single-pixel images and the like. To arrange this, bind the following variable for the duration of such processing.
If this variable is non-
nilnew network connections are never opened by the URL library.
The library can maintain a global history list tracking URLs accessed.
URL completion can be done from it. The history mechanism is set up
url-do-setup when it is configured to be on.
Note that the size of the history list is currently not limited.
This function updates the history table with an entry for url accessed at the given time.
nil, the library will keep track of all the URLs accessed. If it is
t, the list is saved to disk at the end of each Emacs session. The default is
The file storing the history list between sessions. It defaults to history in
Parses the history file fname (default
url-history-file) and sets up the history list.
Saves the current history to file fname (default
You can use this function to do completion of URLs from the history.
The following user options affect the general operation of
The default value specifies a subdirectory named url/ in the standard Emacs user data directory specified by the variable
user-emacs-directory(normally ~/.emacs.d). However, the old default was ~/.url, and this directory is used instead if it exists.
The function to use for asking yes or no functions. This is normally either
yes-or-no-p, but could be another function taking a single argument (the prompt) and returning
tonly if an affirmative answer is given.
A symbol specifying the type of gateway support to use for connections from the local machine. The supported methods are:
- Run telnet in a subprocess to connect;
- Rlogin to another machine to connect;
- Connect through a socks server;
- Connect with SSL;
- Connect directly.
The User Agent string used for sending HTTP/HTTPS requests. The value should be
nil, which means that no ‘User-Agent’ header is generated,
default, which means that a string is generated based on the setting of
url-privacy-leve, a string or a function of no arguments that returns a string.
The default is
default, which means that the ‘User-Agent: package-name URL/Emacs’ string will be generated, where package-name is the value of
url-package-nameand its version, if they are non-
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If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:
- Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
- List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
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- Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
- Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
- Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
- Include an unaltered copy of this License.
- Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
- Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
- For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
- Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
- Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
- Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
- Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.
You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.
- COMBINING DOCUMENTS
You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”
- COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.
- AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.
If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.
You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.
Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.
- FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See https://www.gnu.org/licenses/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document.
“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.
“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.
“Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.
An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.
ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:
Copyright (C) year your name. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:
with the Invariant Sections being list their titles, with the Front-Cover Texts being list, and with the Back-Cover Texts being list.
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
Command and Function Index
url-attributes: Parsed URIs
url-cache-create-filename-human-readable: Disk Caching
url-cache-create-filename-using-md5: Disk Caching
url-cache-expired: Disk Caching
url-encode-url: URI Encoding
url-fetch-from-cache: Disk Caching
url-filename: Parsed URIs
url-fullness: Parsed URIs
url-generic-parse-url: URI Parsing
url-hexify-string: URI Encoding
url-host: Parsed URIs
url-http-options: HTTP URL Options
url-open-stream: Gateways in general
url-password: Parsed URIs
url-port: Parsed URIs
url-queue-retrieve: Retrieving URLs
url-recreate-url: URI Parsing
url-retrieve: Retrieving URLs
url-retrieve-synchronously: Retrieving URLs
url-target: Parsed URIs
url-type: Parsed URIs
url-unhex-string: URI Encoding
url-user: Parsed URIs
socks-nslookup-program: Gateways in general
socks-password: Gateways in general
socks-server: Gateways in general
socks-timeout: Gateways in general
socks-username: Gateways in general
url-automatic-caching: Disk Caching
url-cache-creation-function: Disk Caching
url-cache-directory: Disk Caching
url-cache-expire-time: Disk Caching
url-gateway-local-host-regexp: Gateways in general
url-gateway-method: Gateways in general
url-gateway-prompt-pattern: Gateways in general
url-gateway-rlogin-host: Gateways in general
url-gateway-rlogin-parameters: Gateways in general
url-gateway-rlogin-user-name: Gateways in general
url-gateway-telnet-host: Gateways in general
url-gateway-telnet-login-prompt: Gateways in general
url-gateway-telnet-parameters: Gateways in general
url-gateway-telnet-password: Gateways in general
url-gateway-telnet-password-prompt: Gateways in general
url-gateway-telnet-user-name: Gateways in general
url-gateway-unplugged: Suppressing network connections
url-mime-charset-string: HTTP language/coding
url-mime-language-string: HTTP language/coding
url-queue-parallel-processes: Retrieving URLs
url-queue-timeout: Retrieving URLs
url-unreserved-chars: URI Encoding
- automounter: nfs
- bugs, HTML: Suppressing network connections
- Cache cleaning: Disk Caching
- Caching: Disk Caching
- character sets: HTTP language/coding
- Cleaning the cache: Disk Caching
- Clearing the cache: Disk Caching
- coding systems: HTTP language/coding
- compressed files: file/ftp
- configuration files: Customization
- DASL: HTTP URL Options
- data URLs: data
- DAV: HTTP URL Options
- debugging: Customization
- dired: file/ftp
- Disk Cache: Disk Caching
- email: mailto
- environment variable: news/nntp/snews
- environment variables: Proxies
- ERC: irc
- File Transfer Protocol: file/ftp
- files: file/ftp
- firewalls: Gateways in general
- FTP: file/ftp
- gateways: Gateways in general
- HTML “bugs”: Suppressing network connections
- Info: info
- Internet Relay Chat: irc
- IRC: irc
- language preferences: HTTP language/coding
- LDAP: ldap
- Lightweight Directory Access Protocol: ldap
- mailto: mailto
- man: man
- MD5: Disk Caching
- network connections, suppressing: Suppressing network connections
- Network File System: nfs
- network news: news/nntp/snews
- news: news/nntp/snews
- NFS: nfs
- NNTP: news/nntp/snews
- nslookup: Gateways in general
- opening a stream: Gateways in general
- P3P: HTTP URL Options
- parsed URI: URI Parsing
- parsed URIs: URI Parsing
- percent encoding: URI Encoding
- Persistent Cache: Disk Caching
- proxies: Proxies
- proxy servers: Proxies
- rcirc: irc
- rlogin: Gateways in general
- rlogin: rlogin/telnet/tn3270
- rsync: Tramp
- scp: Tramp
- snews: news/nntp/snews
- socks: Gateways in general
- ssh: Tramp
- stream, opening: Gateways in general
- suppressing network connections: Suppressing network connections
- telnet: Gateways in general
- telnet: rlogin/telnet/tn3270
- terminal emulation: rlogin/telnet/tn3270
- Texinfo: info
- tn3270: rlogin/telnet/tn3270
- uniform resource identifier: Introduction
- uniform resource locator: Introduction
- Unix man pages: man
- unparsing URLs: URI Parsing
- unreserved characters: URI Encoding
- URI: Introduction
- URL: Introduction
- usenet: news/nntp/snews
- ZEN IRC: irc
 Proxies (which only operate over HTTP) are implemented using this.