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Very often, you want to generate multiple versions of the same document:one version for printing and one for viewing on the screen, one version forstudents and one version for the instructor, and so on. You can do this in asimple but naive way: create different files set up for the different versions and< [[Project structure]]code>\input</code> the common material, or create some new conditional flags using<code>\newif</code> and set them appropriately for conditional processing. Or youcould use <em>modes</em>&mdash;the ConTeXt way of doing conditional processing.

ConTeXt supports such filtering A mode is similar to a conditional flag, but with its '''a few advantages: new modes''':need not be explicitly defined (no need for something like <code>\newif</code>),multiple modes can be simultaneously enabled or disabled, and the status of multiplemodes can be checked easily. Moreover, modes can be set from a command lineswitch. As a result, multiple versions of a document can be generated without changingthe source file.

The name or identifier of a mode can be any combination of letters, digits, orspaces. Names starting with <code>*</code> are reserved for system modes.  In this article I explain how to activate a mode and how to check if a mode isactive or not.  = Setting modes = ConTeXt has three commands for setting modes: * <code>{{cmd|enablemode }}[...]</code>* <code>{{cmd|disablemode}}[...]</code>* <code>{{cmd|preventmode}}[...]</code> The names are self-descriptive. {{cmd|enablemode}} activates a mode,{{cmd|disablemode}} deactivates a mode, and {{cmd|preventmode}} permanentlydeactivates a mode. All three commands take a list of modes as an argument. Forexample, you can activate modes named <code>screen</code> and <code>solution</code> with<texcode>\enablemode[screen,solution]<pre/texcode> Modes can also be activated by a command line switch <code>--modes</code> to<code>texexec</code> or <code>context</code>. For example, another way to activate the <code>screen</code> and<code>solution</code> modes, to run ConTeXt using one of:  texexec --mode=screen,solution ... context --mode=screen,solution ... == Pre-defining modes == Normally, the overhead for testing modes is negligible, but it can add up if modes are tested multiple times in a document (for example, as part of a great TeX macro package). In such cases, you can ''define'' a mode before using them, to speed up the processing. Modes are defined using: <texcode>\definemode[...][...]</texcode> The first argument is a list of modes; the second argument may be `yes`, `no`, or `keep`. For example, * <code>\definemode[screen][yes]</code> defines a mode and enables it; * <code>\definemode[screen][no]</code> defines a mode and disables it; * <code>\definemode[screen][keep]</code> defines a mode and keeps its previous status. Typically, it is better to use <code>\definemode[...][keep]</code> so that the modes may be enabled or disabled from command line as well. = Conditional processing based on modes = You may want to process or ignore a chunk of code if a particular mode is enabledor disabled. Such a chunk of code is specified using <code>\startmode</code> and<code>\startnotmode</code> environments. Their use is best explained by an example. Suppose you want to change the paper size of a document depending on whether itis for print or screen. This can be done in multiple ways. You could setthe default paper size for print and change it in screen mode:<texcode>\setuppapersize[letter][letter]\startmode[screen] \setuppapersize[S6][S6]\stopmode</texcode>(S6 is one of the screen-optimized paper sizes in ConTeXt; the paper size has a4:3 aspect ratio and a width equal to the width of A4 paper.) Alternatively, youcould set a default paper size for the screen and change it if screen mode isnot enabled:<texcode>\setuppapersize[S6][S6]\startnotmode[screen] \setuppapersize[letter][letter]\stopnotmode</texcode> <code>\startmode</code> (and <code>\startnotmode</code>) checks the value of the mode '''at the time it is executed'''. This is important when you are setting the modes using <code>\enablemode</code> or <code>\disablemode</code>. For example,<texcode>\enablemode[foo]\startmode[foo]...\stopmode</texcode>the contents of the mode environment are executed because <code>foo</code> is enabled when <code>\startmode</code> is encountered.However, in<texcode>\startmode[handoutfoo]...\stopmode\enablemode[foo] % </texcode>the contents of the mode environment are not execited because <code>foo</code> is not enabled when <code>\startmode</code> is encountered.   == Checking for multiple modes (<code>or</code>/<code>and</code> statements for modes) ==<code>\startmode</code> and <code>\startnotmode</code> can check for multiple modes,by giving a list of modes as their arguments. <code>\startmode</code>processes its contents (everything until the next<code>\stopmode</code>, thus <code>\startmode</code> cannot benested.) if any of the modes are enabled, otherwise (i.e., when allthe modes are disabled) <code>\startmode</code> ignores itscontents. The following text will opposite is <code>\startnotmode</code>: it processes itscontents (everything until the next <code>\stopnotmode</code>) if any of themodes are disabled, otherwise&mdash;when all the modes are enabled&mdash;the contents are ignored. <code>\startmode</code> and <code>\startnotmode</code> are "<em>or</em>" environments. Theyprocess their contents if any of the modes satisfy the required condition. Their"<em>and</em>" counterparts are also available: <code>\startallmodes</code> and <code>\startnotallmodes</code>process their contents only appear in if all the given modes satisfy the handoutrequiredIt’s based on PlainTeX like condition. For example, suppose you want to enable interaction (e.g., hyperlinks)only when both <code>screen</code> and <code>solution</code> modes are enabled. Then you canuse:<texcode>\startallmodes[screen,solution] \setupinteraction[state=start]\stopallmodes</texcode> To summarize, the better known LaTeXfour start-stop environments for checking modes are:<texcode>\startmode[mode1, mode2, ...] % Processed if any of the modes is enabled

<pre>\startnotmode[print]Here's a link to my homepage: \url[mode1, mode2, ...] % Processed if any of the modes is disabled

\startallmodes[mode1, mode2, ...] % Processed if all the modes are enabled\stopallmodes \startnotallmodes[mode1, mode2, ...] % Processed if all the modes are disabled\stopnotallmodes<tt/texcode> These environments have <code>\doif...</code> alternatives that are useful for shortsetups. Also, they can be nested. <texcode>\doifmode {mode1, mode2, ...} {Processed if any modeis enabled}\doifnotmode {mode1, mode2, ...} {Processed if any mode is disabled}\doifallmodes {mode1, mode2, ...} {Processed if all modes are enabled}\doifnotallmodes {mode1, mode2, ...} {Processed if all modes are disabled}</texcode>The logic for determining when the content is processed is exactly the same asfor the <code>start</code>-<code>stop</code> commands. These <code>\doif</code> commands each have a variant to process alternative code ifthe conditions are not satisfied (like the <code>\else</code> branch of <code>\if</code>).<texcode>\doifmodeelse {mode1, mode2, ...} {Processed if any mode is enabled} {else this is processed} \doifallmodeselse {mode1, mode2, ...} {Processed if all modes are enabled} {else this is processed} \doifnotallmodeselse {mode1, mode2, ...} {Processed if all modes are disabled} {else this is processed}</texcode> Note that there is no command <code>\doifnotmodeelse</code> because there is no need for it; <code>\doifmodeelse</ttcode> may be used for the same effect (with the <code>if</code> and <ttcode>else</code> branches switched). == Checking multiple modes in parallel (<code>case</code> statement for modes) == In addition to the above <em>"or"</em> and <em>"and"</em> environment which check modes is sequence, you can also check multiple modes in parallel. The syntax for such a <em>"case"</em> environment is as follows: <texcode>\startmodeset [mode1, mode2, ...notmode] {Processed if either mode is enabled} [mode3, mode4, ...] {Processed if either mode is enabled} [default] {Processed if none of the above modes match}\stopmodeset</tttexcode> let  The same mode can be referenced multiple times, and '''all''' matching branches are executed. The {{cmd|startmodeset}} ... {{cmd|stopmodeset}} environments can be nested. So, you filter your content sufficient can use  <texcode>\startmodeset [mode1, mode2] { Processed when either mode1 or mode2 is enabled } [mode3] { \startmodeset [mode1] {Processed when mode1 and mode3 are enabled} [mode2] {Processed when mode2 and mode3 are enabled} [default] {Processed when mode3 is enabled and mode1 and mode2 are disabled} \stopmodeset } [default] { Processed when mode1, mode2, and mode3 are disabled.: }\stopmodeset</texcode> == Checking modes in Lua == In MkIV, the state of any mode is accessible at the Lua end as <code>tex.modes</code> table. Specifically, <texcode>tex.modes["screen"]</texcode> returns <code>true</code> if mode <code>screen</code> is enabled and <code>false</code> otherwise. Thus, specific combinations of modes can be checked using boolean expressions. For example<texcode>if (tex.modes["mode1"] and tex.modes["mode2"]) then ...end</texcode>checks if both <code>mode1</code> and <code>mode2</code> are enabled.  = System modes = Besides allowing user-definable modes, ConTeXt provides some systemmodes. These modes start with a <code>*</code> character. Here only the more commonly used system modes are explained; see the ConTeXt [http://pragma-ade.com/general/manuals/mmodes.pdf modes manual]for a complete list.  {|cellpadding="5" style="border-collapse: collapse;border-width: 1px; border-style: solid;"|'''*mkii'''| Enabled when running [[MkII]] |-| '''*mkiv''' | Enabled when running [[MkIV]]|}   Perhaps the most useful system modes are <code>*mkii</code> and <code>*mkiv</code> whichdetermine whether MKII or MKIV is being used. These modes are handy when youwant different setups for MKII and MKIV. Other modes are useful for very specific situations. Some of these are describedbelow.   {|cellpadding="5" style="border-collapse: collapse;border-width: 1px; border-style: solid;"| '''*first'''| Enabled during the first compile run|} A document must be run multiple times to get the cross referencing,table of contents, etc.right. However, sometimes you need to do some external processing (e.g., graphicconversion) that only needs to be done once. In such cases, the<code>*first</code> mode is handy&mdash;it is active only on the first run of thedocument.    {|cellpadding="5" style="border-collapse: collapse;border-width: 1px; border-style: solid;"| '''*export'''| Enabled when <code>\setupbackend[export=yes]</code> is set|} You may want to use different images for XML [Export]. The <code>*export</code> mode is useful in such cases.     {|cellpadding="5" style="border-collapse: collapse;border-width: 1px; border-style: solid;"|'''*project'''| Enabled when inside <code>\startproject</code> ... <code>\stopproject</code>|-|'''*component'''| Enabled when inside <code>\startcomponent</code>...<code>\stopcomponent</code>|-| '''*environment'''| Enabled when inside <code>\startenvironment</code> ... <code>\stopenvironment</code>|-| '''*text'''| Enabled when inside <code>\starttext</code> ... <code>\stoptext</code>.|} You can use the project-product-component structure for managing large projectslike a book series. See [[Project structure]]for details of this approach. A product or its components may be compiledseparately, and you may want to do something different when a product iscompiled or when a component is compiled. To do so, you need to check formodes <code>*project</code>, <code>*product</code>, <code>*component</code>, and<code>*environment</code>; these modes are set when the corresponding structure fileis processed. For example, the <code>*product</code> mode is set whenever aproduct file is read; more specifically, when <code>\startproduct</code> isencountered. Similarly, a mode <code>*text</code> is enabled when<code>\starttext</code> is encountered, and likewise for the others.   {|cellpadding="5" style="border-collapse: collapse;border-width: 1px; border-style: solid;"|'''*frontpart''' | Enabled when inside <code>\startfrontmatter</code> ... <code>\stopfrontmatter</code>|-| '''*bodypart'''| Enabled when inside <code>\startbodymatter</code> ... <code>\stopbodymatter</code>|-| '''*backpart'''| Enabled when inside <code>\startbackmatter</code> ... <code>\stopbackmatter</code>|} A large document is typically broken down into different section blocks:frontmatter, bodymatter, appendices, and backmatter. Internally, these sectionblocks are referred to as <code>frontpart</code>, <code>bodypart</code>, <code>appendix</code>, and<code>backpart</code>. Each section block sets a system mode with the same name. So,if you want macros that work differently in different section blocks, you cancheck for modes <code>*frontpart</code>, <code>*bodypart</code>, and so on.   {|cellpadding="5" style="border-collapse: collapse;border-width: 1px; border-style: solid;"|'''*list'''| Enabled inside a list entry|-|'''*marking'''| Enabled inside a marking|-|'''*register'''| Enabled inside a register|-|'''*chapter''', '''*section''', etc.| Enabled inside the corresponding section head.|}  Sometimes you want a macro to behave differently if it is part of a section head, a section number, a list, a marking, or a register. For section heads, you can check for modes <code>*chapter</code>, <code>*section</code>, <code>*subsection</code>, etc. Similarly, <code>*list</code> is enabled inside a list, <code>*marking</code> is enabled inside a marking, and <code>*register</code> is enabled inside a register.   {|cellpadding="5" style="border-collapse: collapse;border-width: 1px; border-style: solid;"|'''*en-us''', '''*nl''', etc.| Enabled when the current <code>\language</code> is <code>en-us</code>, <code>nl</code>, etc.|-|'''**en-us''', '''**nl''', etc.| Enabled when the <code>\mainlanguage</code> is <code>en-us</code>, <code>nl</code>, etc.|} ConTeXt provides support for multiple languages. Languages are recognized bytheir IETF language tags, like <code>en-us</code> for USEnglish, <code>en-gb</code>for British English, <code>nl</code> for Dutch, <code>de</code> for German, etc. A documenthas a main language, set with the command <code>\mainlanguage[...]</code>,that is used fortranslated labels like <em>chapter</em> and <em>figure</em>. You can also give several switch thecurrent language using <code>\language[...]</code> to change the hyphenation rules.Whenever a language is chosen, its identifier is set as a mode. The mode for the mainlanguage starts with two <code>*</code>. For example, when the main languageis USEnglish and the current language is Dutch, the modes <code>**en-us</code> and<code>*nl</code> are set (notice the extra <code>*</code> in <code>**en-us</code>).    {|cellpadding="5" style="border-collapse: collapse;border-width: 1px; border-style: solid;"|'''*figure'''| Enabled when a graphic is found|-|'''*interaction'''| Enabled when interaction is enabled|-|'''*grid'''| Enabled when grid typesetting is enabled|} {|cellpadding="5" style="border-collapse: collapse;border-width: 1px; border-style: solid;"|'''*pdf'''| Enabled when the main output is pdf|-|'''*dvi'''| Enabled when the main output is dvi|} Other system modes like : <code>*figure</code> is set when a graphic is found,<code>*interaction</code> is set when interaction is enabled, <code>*grid</code>is set when grid typesetting is enabled, and <code>*pdf</code> and <code>*dvi</code> are set when the output is PDF or DVI. Othersare too esoteric to describe here. If you are interested, see the modes manual mentioned earlier. = Specific Examples = == Different fonts == Suppose you want to generate two versions of a document, one with times font and one with palatino. One way to do this is as follows: <tttexcode>\startmode[handoutpalatino] \setupbodyfont[palatino,print12pt]\stopmode \startmode[times] \setupbodyfont[postscript,12pt]\stopmode \starttext\input knuth\stoptext</tttexcode>and run with one of the following:  context --mode=palatino filename context --mode=times filename == Running external commands once == Suppose you want to run some external program, say to generate a figure. Unfortunately, the program only generates postscript figure. So you want to convert it to pdf. This can be done as follows:<texcode>\startmode[*first] % external program which creates a file fig-1.ps \executesystemcommand{some_external_program ...} % convert PS into PDF \executesystemcommand{texmfstart pstopdf fig-1.ps}\stopmode

You can typeset % include the different modes like:resulting PDF\externalfigure[fig-1]</texcode>