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diff --git a/doc/field-roles.rst b/doc/field-roles.rst new file mode 100644 index 000000000000..3499aea81aba --- /dev/null +++ b/doc/field-roles.rst @@ -0,0 +1,317 @@ + +.. index:: Field Roles +.. _field-roles: + +Field Roles +~~~~~~~~~~~ + +Field roles are optional, and indicate the role and formatting of the +content. The roles are listed below; only one role is permitted: + + === ============== ================================================= + R Name Description + === ============== ================================================= + C color Field has color and effect controls + D decoration Field is non-text (e.g., colon, comma) + E error Field is an error message + G gettext Call gettext(3) on the format string + L label Field is text that prefixes a value + N note Field is text that follows a value + P padding Field is spaces needed for vertical alignment + T title Field is a title value for headings + U units Field is the units for the previous value field + V value Field is the name of field (the default) + W warning Field is a warning message + [ start-anchor Begin a section of anchored variable-width text + ] stop-anchor End a section of anchored variable-width text + === ============== ================================================= + +:: + + EXAMPLE: + xo_emit("{L:Free}{D::}{P: }{:free/%u} {U:Blocks}\n", + free_blocks); + +When a role is not provided, the "*value*" role is used as the default. + +Roles and modifiers can also use more verbose names, when preceded by +a comma:: + + EXAMPLE: + xo_emit("{,label:Free}{,decoration::}{,padding: }" + "{,value:free/%u} {,units:Blocks}\n", + free_blocks); + +.. index:: Field Roles; Color +.. _color-role: + +The Color Role ({C:}) ++++++++++++++++++++++ + +Colors and effects control how text values are displayed; they are +used for display styles (TEXT and HTML):: + + xo_emit("{C:bold}{:value}{C:no-bold}\n", value); + +Colors and effects remain in effect until modified by other "C"-role +fields:: + + xo_emit("{C:bold}{C:inverse}both{C:no-bold}only inverse\n"); + +If the content is empty, the "*reset*" action is performed:: + + xo_emit("{C:both,underline}{:value}{C:}\n", value); + +The content should be a comma-separated list of zero or more colors or +display effects:: + + xo_emit("{C:bold,inverse}Ugly{C:no-bold,no-inverse}\n"); + +The color content can be either static, when placed directly within +the field descriptor, or a printf-style format descriptor can be used, +if preceded by a slash ("/"): + + xo_emit("{C:/%s%s}{:value}{C:}", need_bold ? "bold" : "", + need_underline ? "underline" : "", value); + +Color names are prefixed with either "fg-" or "bg-" to change the +foreground and background colors, respectively:: + + xo_emit("{C:/fg-%s,bg-%s}{Lwc:Cost}{:cost/%u}{C:reset}\n", + fg_color, bg_color, cost); + +The following table lists the supported effects: + + =============== ================================================= + Name Description + =============== ================================================= + bg-XXXXX Change background color + bold Start bold text effect + fg-XXXXX Change foreground color + inverse Start inverse (aka reverse) text effect + no-bold Stop bold text effect + no-inverse Stop inverse (aka reverse) text effect + no-underline Stop underline text effect + normal Reset effects (only) + reset Reset colors and effects (restore defaults) + underline Start underline text effect + =============== ================================================= + +The following color names are supported: + + ========= ============================================ + Name Description + ========= ============================================ + black + blue + cyan + default Default color for foreground or background + green + magenta + red + white + yellow + ========= ============================================ + +When using colors, the developer should remember that users will +change the foreground and background colors of terminal session +according to their own tastes, so assuming that "blue" looks nice is +never safe, and is a constant annoyance to your dear author. In +addition, a significant percentage of users (1 in 12) will be color +blind. Depending on color to convey critical information is not a +good idea. Color should enhance output, but should not be used as the +sole means of encoding information. + +.. index:: Field Roles; Decoration +.. _decoration-role: + +The Decoration Role ({D:}) +++++++++++++++++++++++++++ + +Decorations are typically punctuation marks such as colons, +semi-colons, and commas used to decorate the text and make it simpler +for human readers. By marking these distinctly, HTML usage scenarios +can use CSS to direct their display parameters:: + + xo_emit("{D:((}{:name}{D:))}\n", name); + +.. index:: Field Roles; Gettext +.. _gettext-role: + +The Gettext Role ({G:}) ++++++++++++++++++++++++ + +libxo supports internationalization (i18n) through its use of +gettext(3). Use the "{G:}" role to request that the remaining part of +the format string, following the "{G:}" field, be handled using +gettext(). + +Since gettext() uses the string as the key into the message catalog, +libxo uses a simplified version of the format string that removes +unimportant field formatting and modifiers, stopping minor formatting +changes from impacting the expensive translation process. A developer +change such as changing "/%06d" to "/%08d" should not force hand +inspection of all .po files. + +The simplified version can be generated for a single message using the +"`xopo -s $text`" command, or an entire .pot can be translated using +the "`xopo -f $input -o $output`" command. + + xo_emit("{G:}Invalid token\n"); + +The {G:} role allows a domain name to be set. gettext calls will +continue to use that domain name until the current format string +processing is complete, enabling a library function to emit strings +using it's own catalog. The domain name can be either static as the +content of the field, or a format can be used to get the domain name +from the arguments. + + xo_emit("{G:libc}Service unavailable in restricted mode\n"); + +See :ref:`i18n` for additional details. + +.. index:: Field Roles; Label +.. _label-role: + +The Label Role ({L:}) ++++++++++++++++++++++ + +Labels are text that appears before a value:: + + xo_emit("{Lwc:Cost}{:cost/%u}\n", cost); + +If a label needs to include a slash, it must be escaped using two +backslashes, one for the C compiler and one for libxo:: + + xo_emit("{Lc:Low\\/warn level}{:level/%s}\n", level); + +.. index:: Field Roles; Note +.. _note-role: + +The Note Role ({N:}) +++++++++++++++++++++ + +Notes are text that appears after a value:: + + xo_emit("{:cost/%u} {N:per year}\n", cost); + +.. index:: Field Roles; Padding +.. _padding-role: + +The Padding Role ({P:}) ++++++++++++++++++++++++ + +Padding represents whitespace used before and between fields. + +The padding content can be either static, when placed directly within +the field descriptor, or a printf-style format descriptor can be used, +if preceded by a slash ("/"):: + + xo_emit("{P: }{Lwc:Cost}{:cost/%u}\n", cost); + xo_emit("{P:/%30s}{Lwc:Cost}{:cost/%u}\n", "", cost); + +.. index:: Field Roles; Title +.. _title-role: + +The Title Role ({T:}) ++++++++++++++++++++++ + +Title are heading or column headers that are meant to be displayed to +the user. The title can be either static, when placed directly within +the field descriptor, or a printf-style format descriptor can be used, +if preceded by a slash ("/"):: + + xo_emit("{T:Interface Statistics}\n"); + xo_emit("{T:/%20.20s}{T:/%6.6s}\n", "Item Name", "Cost"); + +Title fields have an extra convenience feature; if both content and +format are specified, instead of looking to the argument list for a +value, the content is used, allowing a mixture of format and content +within the field descriptor:: + + xo_emit("{T:Name/%20s}{T:Count/%6s}\n"); + +Since the incoming argument is a string, the format must be "%s" or +something suitable. + +.. index:: Field Roles; Units +.. index:: XOF_UNITS +.. _units-role: + +The Units Role ({U:}) ++++++++++++++++++++++ + +Units are the dimension by which values are measured, such as degrees, +miles, bytes, and decibels. The units field carries this information +for the previous value field:: + + xo_emit("{Lwc:Distance}{:distance/%u}{Uw:miles}\n", miles); + +Note that the sense of the 'w' modifier is reversed for units; +a blank is added before the contents, rather than after it. + +When the XOF_UNITS flag is set, units are rendered in XML as the +"units" attribute:: + + <distance units="miles">50</distance> + +Units can also be rendered in HTML as the "data-units" attribute:: + + <div class="data" data-tag="distance" data-units="miles" + data-xpath="/top/data/distance">50</div> + +.. index:: Field Roles; Value +.. _value-role: + +The Value Role ({V:} and {:}) ++++++++++++++++++++++++++++++ + +The value role is used to represent the a data value that is +interesting for the non-display output styles (XML and JSON). Value +is the default role; if no other role designation is given, the field +is a value. The field name must appear within the field descriptor, +followed by one or two format descriptors. The first format +descriptor is used for display styles (TEXT and HTML), while the +second one is used for encoding styles (XML and JSON). If no second +format is given, the encoding format defaults to the first format, +with any minimum width removed. If no first format is given, both +format descriptors default to "%s":: + + xo_emit("{:length/%02u}x{:width/%02u}x{:height/%02u}\n", + length, width, height); + xo_emit("{:author} wrote \"{:poem}\" in {:year/%4d}\n, + author, poem, year); + +.. index:: Field Roles; Anchor +.. _anchor-role: + +The Anchor Roles ({[:} and {]:}) +++++++++++++++++++++++++++++++++ + +The anchor roles allow a set of strings by be padded as a group, +but still be visible to xo_emit as distinct fields. Either the start +or stop anchor can give a field width and it can be either directly in +the descriptor or passed as an argument. Any fields between the start +and stop anchor are padded to meet the minimum width given. + +To give a width directly, encode it as the content of the anchor tag:: + + xo_emit("({[:10}{:min/%d}/{:max/%d}{]:})\n", min, max); + +To pass a width as an argument, use "%d" as the format, which must +appear after the "/". Note that only "%d" is supported for widths. +Using any other value could ruin your day:: + + xo_emit("({[:/%d}{:min/%d}/{:max/%d}{]:})\n", width, min, max); + +If the width is negative, padding will be added on the right, suitable +for left justification. Otherwise the padding will be added to the +left of the fields between the start and stop anchors, suitable for +right justification. If the width is zero, nothing happens. If the +number of columns of output between the start and stop anchors is less +than the absolute value of the given width, nothing happens. + +.. index:: XOF_WARN + +Widths over 8k are considered probable errors and not supported. If +XOF_WARN is set, a warning will be generated. |