$NAME(1)

NAME
$NAME - Fast and lightweight Usenet client with GUI

SYNOPSIS
$NAME [-display [host]:display] [-geometry WxH[+X+Y]]

$NAME [-h|-v]

DESCRIPTION
If you don't know what Usenet is, you probably want to read this article first:

https://en.wikipedia.org/wiki/Usenet

$NAME is a client with graphical user interface that uses the NNTP protocol defined in RFC 3977 to get Usenet news articles defined in RFC 5536 from a server via IP network. Version 1 of the NNTP protocol (as defined in RFC 977) is supported too and automatically used, if the server does not report support for Version 2.

If compiled with support for ssl(3), the NNTPS protocol (NNTP over encrypted TLS connection) is supported. For NNTPS connections the server to client authentication via X509 certificate is always performed. Optionally the client can authenticate to the server via the AUTHINFO USER/PASS extension defined in RFC 4643.

If compiled with support for compression and zlib(3), the NNTP COMPRESS extension is supported. Compression negotiation is disabled by default and can be enabled on the 'Edit->Configuration->Misc' tab in the user interface. Because compression in general can weaken the underlaying encryption, the optional authentication is always done before compression is negotiated. For the same reason compression negotiation should be disabled for reading groups that contain articles with confidential information.

$NAME provides full Unicode support, including NFC normalization for posting and search/compare operations. Article content is converted to ISO 8859-1 before posting (if possible) to be more friendly to old clients. The ability to display Unicode content depends on the GUI toolkit fltk(3). Even if the content could not be correctly displayed, it is always possible to correctly quote it in follow-up articles.

$NAME has MIME support according to RFC 2045, RFC 2046, RFC 2047 and RFC 2231. Since version 0.18 full MIME conformance according to RFC 2049 Section 2 was reached. Posted articles should be fully RFC 5536 conformant (without postprocessing by the user).

Additional checks are implemented that create warnings if an article violates common Usenet conventions. Conformance to mandatory GNKSA 2.0 rules was reached with exception of part 4 (the "Reply-To" header field can only be modified before the article composer is started):

https://gnksa.org/

Currently $NAME $VERSION provides no support for the following features:

•   Multiple servers

•   Offline mode

•   UUCP

If you need one of these features, use leafnode(8) or another proxy server (consider Hamster for machines with Windows operating system).

OPTIONS
The following options are supported:

-4  Force usage of IPv4 network protocol.

-confprefix path
    Use different configuration directory (specify path without trailing slash).

    Attention: Never set path to an existing configuration directory for $NAME with a different major version number!

-debug
    Enable debug mode.

    Additional messages are printed to the terminal via stderr.

    The network communication with the NNTP server is logged. See "logfile" in the FILES section.

-display [host]:display
    X display to use. More information about X can be found in X(7).

-geometry WxH[+X+Y]
    Window size and position.

-h  Print help message.

-iconic
    Starts with minimized window.

-notooltips
    Disable tooltip messages.

-v  Print version information and compile time options.

    Compile time options:

    •   CLB (POSIX.2 C Language Binding)

    •   FSC (POSIX.1 File Synchronization option)

    •   IP6 (Internet Protocol V6)

    •   NLS (National Language Support)

    •   P2K (POSIX.1-2001 or newer)

    •   TLS (Transport Layer Security)

    •   XSI (X/Open System Interface extension)

    •   ZLIB (DEFLATE compression algorithm)

EXIT STATUS
Zero on regular exit. All other values indicate an error.

ENVIRONMENT

DISPLAY
    X display to use. More information about X can be found in X(7).

FLTK_SCHEME
    Selects the FLTK scheme to use. FLTK 1.3.0 accepts the following options:

    •   none (Default style)

    •   gtk+ (GTK+ style)

    •   plastic (Aqua style)

    Newer FLTK versions may accept additional schemes.

TMPDIR
    Directory used for temporary files (as recommended by POSIX). This value will override the default "/tmp".

TZ  The timezone that is used by localtime(3). $NAME internally uses this function to convert POSIX timestamps to local time and for creating 'date-time' tokens according to RFC 5322.

XDG_CONFIG_HOME
    Prefix for configuration directory path according to XDG Base Directory Specification. This value will override the default "~/.config". The program name $NAME is appended as last path component.

In addition, $NAME honours the following locale related variables:

LANG
    Used as fallback if LC_* variables are not set.

LC_ALL
    Overdrives all other LC_* variables.

LC_CTYPE
    Character classification to use. Only locales with US-ASCII, ISO 8859-1 and UTF-8 codesets are allowed here. Setting this to a locale with UTF-8 codeset is very expensive on some operating systems (e.g. more than an order of magnitude slower on NetBSD 5). Note that setting this to POSIX or an ISO 8859-1 locale will not completely disable Unicode support! You can at least use Unicode for your name in the identity configuration and you can correctly quote Unicode content for follow-up articles in any case.

LC_MESSAGES
    Locale for user interface language. The codeset is ignored because FLTK internally always use UTF-8 (regardless of the locale settings). If $NAME is compiled without National Language Support (NLS), this variable is ignored.

As a general rule, POSIX.2 define that all locale sections must use the same codeset. More information about NLS can be found in nls(7) or locale(7) depending on the operating system.

X RESOURCES
Information about X resources and how to set them can be found in X(7).

fltk.background
    (String) The value of this ressource is taken as the background color for most widgets (see Text.background if it does not work).

fltk.foreground
    (String) The value of this ressource is taken as the foreground color for most widgets.

fltk.scheme
    (String) See the environment variable FLTK_SCHEME for possible values. The environment variable takes precedence over this ressource.

Text.background
    (String) The value of this ressource is taken as the background color for text, list, and valuator widgets.

Text.selectBackground
    (String) The value of this ressource is taken as the background color for selected text. Set it to something like "gray" for a more decent selection color. On machines with 8-bit color depth the highlight color for search results (that is derived from the selection background color) may have little or no contrast. Use a darker color in this case, e.g. "darkgray".

Xft.antialias
    (Boolean) If FLTK uses the X11 backend and is compiled to use Xft (the default), then the value "true" will enable and "false" will disable font anti-aliasing. The recommended setting is "true".

Xft.hinting
    (Boolean) If FLTK uses the X11 backend and is compiled to use Xft (the default), then the value "true" will enable and "false" will disable font hinting. The recommended setting is "true".

Xft.autohint
    (Boolean) If FLTK uses the X11 backend, is compiled to use Xft (the default) and Xft is configured with enabled font hinting (resource Xft.hinting set to "true") then this resource controls the hinting algorithm. With setting "false" the BCI algorithm is used, "true" enables the builtin autohinter of Freetype2. The recommended setting is "false".

Xft.hintstyle
    (Integer) If FLTK uses the X11 backend, is compiled to use Xft (the default) and Xft is configured with enabled font hinting (resource Xft.hinting set to "true") then this resource controls the hinting mode. Possible values are "hintnone" (0), "hintslight" (1), "hintmedium" (2) and "hintfull" (3). The recommended setting is "hintfull" (3).

    Attention: With some modes it is possible that lines will overlap and characters like underscore are clipped!

FILES

~/.signature
    The signature from this file is automatically appended to all created articles.
    This file is not used if another location for the signature file is configured. See CONFIGURATION section below for details (configfile entry "signature_file").

    Note: At this (shared) location the file should be US-ASCII encoded. If you want to use Unicode in signatures, a dedicated signature file for $NAME should be configured.

The following files are inside the configuration directory. The default location is "~/.config/$NAME". The environment variable XDG_CONFIG_HOME and the option -confprefix (highest precedence) can be used to modify the configuration directory location.

.cancelsecret
    Secret for generating Cancel-Locks/-Keys with scheme SHA256 according to RFC 8315.
    The secret in this file must be a cryptographically random value according to RFC 4086 and should be at least 32 octets in length.

    $NAME must be compiled with support for ssl(3) or this file will be ignored, because the cryptographic functions are shared.

    If this file is not present, it is automatically created and a new secret is written to it (using random data from the cryptographic PRNG).

    If this file is present and not empty, and the fqdn entry is set, $NAME creates "Cancel-Lock" (always) and "Cancel-Key" header fields when canceling or superseding articles.

    To use the same secret as another installation of $NAME (or another newsreader that use the algorithm recommended by RFC 8315 with HMAC based on SHA256), copy the file with the desired secret to this location.

    To manually disable this feature, an empty file must be used.

    Attention: Everybody who get his hands on this secret can cancel articles that were locked using this key in the past! This file should be readable only by the user.

    The old scheme SHA1 is still supported too. See CONFIGURATION section below for details (configfile entry "cancelkey").

configfile
    Configuration and user interface state of last session. The file format is forward and backward compatible between all versions with same major number.

    See CONFIGURATION section below for details.

groupfile
    Subscribed groups and already viewed articles database. The data is US-ASCII encoded in newsrc format and can be shared with other newsreaders using the entry newsrc in configfile. It is possible to share the group data over machine borders by using a NFS server (advisory file locking support is required).

    Attention: In any case all newsreaders that share a groupfile must be configured to use the same server! There is a convention to name such files "newsrc-$HOSTNAME" to make it obvious for which server they can be used.

    It is allowed to share the groupfile between multiple instances of $NAME that run simultaneously. The file will contain the state of the instance that is terminated last.

headers/*
    Cached article header database. The file names correspond to the article watermarks of the current NNTP server. If the server provides the OVER capability defined in RFC 3977, this database is not used.

    Overview usage can be explicitly disabled. See CONFIGURATION section below for details (configfile entry "nntp_no_over").

logfile
    Protocol dump of server communication from current/last session. To view this data while the program is running, select 'Tools->Protocol console' in the user interface. This file is overwritten for every new connection.

    Only enabled in debug mode. See "-debug" in the OPTIONS section.

scorefile
    Scoring rules. The file format is forward and backward compatible between all versions with same major number. The data can be shared using the entry scorerc in configfile. It is possible to share the scoring rules over machine borders by using a NFS server (advisory file locking support is required).

    It is allowed to share the scorefile between multiple instances of $NAME that run simultaneously. The file will contain the state of the instance that is terminated last.

    See SCORING section below for details.

CONFIGURATION
This section describes the format of the configfile.

This file must be a POSIX textfile, this means every line must be terminated with a LF line break.

Any line starting with '#' is treated as a comment (not parsed and ignored). Missing entries are automatically added, unsupported entries are ignored.

The content can have one of two types: Integer or Unicode string. Strings use the UTF-8 representation and NFC normalization of Unicode.

The following entries are supported by version $VERSION but can't be configured from the GUI. Some have no GUI editor by intent. If you don't know what you are doing, consider to not modify them.

•   cancelkey (String) Secret for generating Cancel-Locks/-Keys with scheme SHA1 according to RFC 8315

    $NAME must be compiled with support for ssl(3) to make this work, because the cryptographic functions are shared.

    If this entry and the fqdn entry are set, $NAME creates "Cancel-Lock" (always) and "Cancel-Key" header fields when canceling or superseding articles.

    Note: The scheme SHA1 is obsolete since RFC 8315. This entry is preserved for backward compatibility. After a transition period this entry should be left empty and the scheme SHA256 should be used. See section above (File "~/.config/$NAME/.cancelsecret").

•   color_xxx (Integer) Text foreground color for xxx.

    The value must be an 8-bit index for the FLTK colormap:

    https://www.fltk.org/doc-1.3/drawing.html#drawing_colors

•   crl_check (Integer) Enable TLS certificate CRL checks

    A nonzero value means that CRL checks are enabled.

    $NAME must be compiled with support for CRL checks to make this work.

•   crl_upd_c (Integer) TLS certificate CRL update choice

    A nonzero value means that, after the CRL update interval has elapsed, the user get a choice to select whether the CRL update should be delayed.

•   crl_upd_iv (Integer) TLS certificate CRL update interval

    The value must be positive and is a period of time in hours. Too large values (longer than one year) are clamped to the upper limit. The value zero means that new CRLs should be downloaded for every new connection (not recommended).

•   crl_upd_ts (String) TLS certificate CRL update timestamp

    This entry contains a timestamp in ISO 8601 format for the last successful CRL update.

•   dist_suggestions (Integer) Use distribution suggestions

    Setting this to a nonzero value automatically initialize the distribution header field in the composer with suggested distribution data (if available). If no distribution suggestions are available for the target groups, the header field is initialized to "world" as with this option set to zero.

    Any time a distribution suggestion is used, the user is informed with a popup window in the GUI.

    With the NNTP protocol the command LIST DISTRIB.PATS is used to retrieve the distribution suggestions from the server.

•   editor (String) Optional external editor for article composition

    The pathname of an executable program must be specified.

    The pathname of a file containing the data is passed as parameter. If the external editor requires additional parameters, a start script must be specified (and the script must provide the additonal parameters).

    The editor must be able to process Unicode data in UTF-8 format. The specified editor must terminate with exit status zero on success.

    A temporary file is used. Consider to set the TMPDIR environment variable.

•   flowed_insert_crlf (Integer) Add empty line after paragraph

    Only used if "Format=flowed" is declared.

    A value of zero corresponds to the dumb behaviour up to version 0.16 (if a paragraph ends with an empty line, there is no separation to the following text).

    A value of one adds an empty line separator after every paragraph that ends with an empty line. This is required to create single line paragraphs (allow single line to be rewrapped to smaller width for display). The author of an article can request this behaviour with the experimental parameter "InsLine=yes" in addition to "Format=flowed".

•   fqdn (String) Fully qualified domain name (FQDN) of the machine

    Must be empty or a valid "dot-atom" according to RFC 5322, this means the nameless root domain must be omitted (no trailing dot).

    This entry is used to generate Message-IDs. They are only worldwide unique for all time if $NAME runs on a machine with a FQDN. In addition the clock of the machine must be synchronized so that timestamps are not ambigous.

    If a FQDN is configured, the header fields "Message-ID", "Injection-Date", "Cancel-Lock" and "Cancel-Key" (only when cancelling or superseding an article) are created by $NAME for all outgoing articles. Note that RFC 5537 specifies some nasty details for the "Injection-Date" header field (they are the reason to handle it internally in this case).

•   force_unicode (Integer) Force Unicode for outgoing articles

    With the value zero outgoing articles are converted to ISO 8859-1 if possible. With a nonzero value, all articles are sent using Unicode (UTF-8 transformation format).

•   immedauth (Integer) Immediate authentication option

    The value one represents the default behaviour to authenticate immediately after a connection was established.

    The value zero switches the behaviour, so that authentication against the server is only executed after a request to do so (480 response when using NNTP protocol).

•   inews (String) Pathname of an optional external inews

    The external inews must accept the article on its standard input and inject it into the network. After successful completion of this task it must terminate with exit status zero. In the case of an error, it must terminate with a nonzero exit status.

    Note that the article feeded into the external inews has canonical format (CR+LF line breaks).

    If your inews needs command line parameters or a different input format, specify a shell script here (and call the external inews from this script).

•   initial_greeting (String) Greeting line for first article of new thread

    The content is automatically inserted into the body of every new regular article (that is not a followup, cancel or supersede).

•   intro (String) Introduction line format

    The name of the cited author can be inserted with "%s". The newsgroups list of the cited article can be inserted with "%g". Every variable is allowed only once.

    The last character should be a colon.

•   inv_order (Integer) Inverse order

    The value zero is the default behaviour (top down).

    A nonzero value inverts the order of articles or thread branches respectively.

•   kill_threshold (Integer) Threshold score to kill articles

    The score of an article is compared to this threshold when it is added to the article tree/list. Articles with a score below this threshold are killed (not displayed).

    The minimum value is -49999 and the maximum value is 0 (kill all articles with negative score).

    The value -9999 is used as default.

    The default score of an article is 0. See SCORING section below how to increase or decrease the score of articles.

•   newsrc (String) Optional pathname of file to share group states in newsrc format

    This file is imported at startup and used as groupfile. At exit the local groupfile is copied back to this location. Note that this file is replaced with rename(2) and is not modified in place. If the file is accessed via NFS, advisory locking must be available.

•   nntp_no_over (Integer) Disable usage of overview (OVER command) for NNTP protocol

    Setting this to a nonzero value disables usage of overview and makes the whole newsgroup list usable for scoring rules.

    If the usage of overview is disabled with a nonzero value (or the server has offered no OVER capability), then article headers are stored in a local database. See "headers/*" in the FILES section.

    In general the default value 0 should be used. There are two scenarios for which this option may be useful.

    If the network connection to the server is very slow and no data compression is available: In this case the transfer of the (larger) overview may be slower than the transfer of a few (smaller) new headers, because the older headers can be taken from the local database.

    If one or more scoring rules should match other (not the current or not subscribed at all) newsgroups in Xposts: Because the newsgroup list is not part of the overview, only the current group is available if the overview is used.

•   organization (String) Optional name of the users organization

    The string is inserted as 'Organization' header field in outgoing articles.

•   post_proc (String) Pathname of an optional article postprocessor

    Note: The postprocessor can be used to insert custom header fields.

    The postprocessor must be a filter in Unix sense. It must accept the article on its standard input, process it and write the result to its standard output. After successful completion of this task, it must terminate with exit status zero. In the case of an error, the postprocessor must terminate with a nonzero exit status.

    Note that the article feeded into the postprocessor has canonical format (CR+LF line breaks) and use Unicode UTF-8 encoding for the body. Modifications must preserve this format. The Unicode normalization, potential conversion to the target character set and the application of the transfer encoding to the body is done after the postprocessing. Therefore the postprocessor is not allowed to add "Content-Type" and "Content-Transfer-Encoding" header fields!

    The header is already in RFC 2047 format. If the postprocessor modifies an existing header field, this format must be preserved. If a new header field is added, the postprocessor is responsible for creating valid RFC 2047 encoding and Unicode normalization to NFC.

•   refresh_interval (Integer) Group list refresh interval

    The value zero is the default behaviour and disables the autorefresh feature.

    A nonzero value refreshes the group list in the specified interval (in minutes).

•   scorerc (String) Optional pathname of file to share scoring rules

    This file is imported at startup and used as scorefile. At exit the local scorefile is copied back to this location. Note that this file is replaced with rename(2) and is not modified in place. If the file is accessed via NFS, advisory locking must be available.

•   signature_file (String) Pathname of file with signature (relative to home directory)

    Default value: ".signature".

    If this file is present, its content is used as signature. The signature separator "dash dash space" plus LF line break is automatically prepended if not already present in this file. The file must be a POSIX text file (LF line break after every line, including the last one) with Unicode encoding in UTF-8 format (Unicode normalization is not important and applied automatically).

    Use an empty string to disable signature generation.

•   testgrp_ere (String) POSIX.2 Extended Regular Rxpression (Unicode is allowed)

    If non US-ASCII characters are used in the regular expression, they must be representable in the codeset of the character classification locale used at runtime. Otherwise the regular expression from this entry is ignored and will never match. See the desciption for the LC_CTYPE environment variable above for details.

    Note that this regular expression is used for matching against individual group names, not group lists. This means '^' and '$' will match start and end of individual group names.

    If a match is detected against a group name, this group is treated as a test group that may require special control commands in the "Keywords" header field to silence e.g. reflector bots (see entry "testgrp_kwords" for keyword configuration).

•   testgrp_kwords (String) Comma separated list of words

    If a target group of an article is identified as a test group (as described for the "testgrp_ere" entry), the header field "Keywords" is initialized to the value defined with this entry.

    Attention: Version $VERSION of $NAME currently only supports US-ASCII keywords. Do not use spaces around commas.

•   timestamp_comment (Integer) Generate Date header field with timezone comment

    The value zero represents the default behaviour to append no comment.

    The value one switches the behaviour, so that a comment with the name of the timezone is appended to the Date header field. If the operating system does not provide timezone information, this entry is ignored.

•   tls_owncerts (Integer) Use local trust anchors for TLS

    With nonzero value the trust anchor (X.509 root certificate) of a certificate chain is searched in the local location only. The system wide certificate store of the OpenSSL installation is ignored.

    Local X.509 certificate path: ~/.config/$NAME/certs

    Copy the root certificate (in PEM format) to a file with arbitrary name in the path specified above. Then run the c_rehash utility to create the symlink that OpenSSL uses for searching.

•   unread_in_next_group (Integer) Skip to next group for unread article

    With zero value searching for next unread article stays in current group.

    With nonzero value the next group with unread articles is selected if there are no more unread articles in the current group.

SCORING
This section describes the format of the scorefile.

This file must be a POSIX textfile, this means every line must be terminated with a LF line break.

Any line starting with '#' is treated as a comment (not parsed and ignored).

Since version 1.3.0 empty lines are ignored. This change is forward compatible (older 1.x versions create parse error messages for empty lines, but preserve them and handle the other lines as expected).

All other lines are parsed as rules with four colon-separated fields:

•   Target The groups to which the rule is associated.

    This must be a wildmat according to RFC 3977. The wildmat "*" will match all groups.

•   Type The header field to which the rule is associated. This field is case sensitive.

    All types with suffix "_ere" use pattern matching with a POSIX Extended Regular Expression (ERE):

    https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html

    The following types (in alphabetical order) are recognized by version $VERSION.

    Type "from": The string from the fourth field must match literally against the "From" header field body.

    Type "from_ere": The string from the fourth field is interpreted as a POSIX.2 ERE and must match against the "From" header field body.

    Type "group": The string from the fourth field must match literally against a group element in the "Newsgroups" header field body.

    Type "msgid_ere": The string from the fourth field is interpreted as a POSIX.2 ERE and must match against the "Message-ID" header field body.

    Type "subject": The string from the fourth field must match literally against the "Subject" header field body.

    Type "subject_ere": The string from the fourth field is interpreted as a POSIX.2 ERE and must match against the "Subject" header field body.

•   Score The score value that apply if the filter rule matches.

    This must be a signed integer value. If the scorefile is shared between multiple instances of $NAME, the values must be usable for the whole group. The machine with the smallest limits will clamp the values if they are too large or too small respectively.

•   String The rules content string.

    This must always be an Unicode string (in UTF-8 format with NFC normalization).

    Attention: If the normalization is wrong, the rule may not match as intended!

    The colon has no special meaning inside this field anymore and must not be quoted for any of the rule types listed above.

Note that rules using wildmats (other than "*") and/or regular expressions are ignored if $NAME is compiled without support for regular expressions.

If non US-ASCII characters are used in a regular expression, they must be representable in the codeset of the character classification locale used at runtime. Otherwise the regular expression from this entry is ignored and will never match. See the desciption for the LC_CTYPE environment variable above for details.

The default score for every article is zero. If a rule matches, the score value from the second field will be added to the corresponding article. Note that the processing is not stopped after a match, the following rules are applied too.

Articles with nonzero score result are marked with icons in the GUI. Articles with negative score result are additionally marked as read.

NOTES
$NAME is based in part on the work of the following projects:

•   FLTK toolkit for graphical user interface (https://www.fltk.org/)

•   Unicode standard for text encoding (https://www.unicode.org/)

    Unicode is a registered trademark of Unicode, Inc. in the United States and other countries.

•   OpenSSL cryptographic libraries (https://www.openssl.org/)

    If compiled with support for TLS.

•   LibreSSL cryptographic libraries (https://www.libressl.org/)

    If compiled with support for TLS (as replacement for OpenSSL).

•   zlib compression library (https://zlib.net/)

    If compiled with support for compression.

AUTHORS
To view the list of authors and the license terms, select 'Help->License' in the user interface.

BUGS
To report bugs, select 'Help->Bug report' in the user interface.

STANDARDS
$NAME tries to comply with the following standards:

ISO 2022, ISO 8601, ISO 8859, RFC 20, RFC 822, RFC 850, RFC 977, RFC 1468, RFC 1738, RFC 2045, RFC 2046, RFC 2047, RFC 2049, RFC 2104, RFC 2152, RFC 2183, RFC 2231, RFC 2246, RFC 2368, RFC 2585, RFC 2606, RFC 2646, RFC 2980, RFC 3174, RFC 3629, RFC 3676, RFC 3977, RFC 3986, RFC 4346, RFC 4642, RFC 4643, RFC 5198, RFC 5246, RFC 5280, RFC 5322, RFC 5536, RFC 5537, RFC 5538, RFC 6048, RFC 6066, RFC 6068, RFC 6176, RFC 6657, RFC 7230, RFC 7231, RFC 7234, RFC 7366, RFC 7507, RFC 7568, RFC 7627, RFC 7919, RFC 8054, RFC 8089, RFC 8143, RFC 8315, RFC 8446, RFC 8996, POSIX.2-1992, POSIX.1-1996, POSIX.1-2001, POSIX.1-2008, Unicode 15.1.0, XDG Base Directory Specification 0.7

SEE ALSO
fltk(3), leafnode(8), locale(7), localtime(3), nls(7), ssl(3), zlib(3), X(7)

https://en.wikipedia.org/wiki/Usenet

https://gnksa.org/

https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html