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{{todo|This FAQ needs to have a lot of things worked on.  To avoid clutter from repeated TODO tags, just note missing answers with "...", and put notes about missing information in parentheses.}}
 
{{todo|This FAQ needs to have a lot of things worked on.  To avoid clutter from repeated TODO tags, just note missing answers with "...", and put notes about missing information in parentheses.}}
 +
 +
== ConTeXt General ==
  
 
=== What is ConTeXt? ===
 
=== What is ConTeXt? ===
:It is a document production system based on Donald Knuth's [[http://www.tug.org/ TeX]].  It is a set of high-level macros written in the (somewhat arcane) TeX language, and these macros simplify the task of designing layouts, making hyperlinks, etc.
 
  
=== Is there a hello-world document? ===
+
: ConTeXt is a document production system, based on Donald Knuth's [http://www.tug.org/ TeX], for typesetting high-quality documents. More specifically, it is both:
:Yes. See [[First Document]] and [[Hello world]].
+
:* a set of high-level macros written in the (somewhat arcane) TeX language, and these macros simplify the task of designing layouts, making hyperlinks, etc.
 +
:* and a set of software and tools for moving from these macros to high-quality digital documents.
 +
: Unlike familiar word processors where the formatting of the final document is crafted while writing the content, ConTeXt documents are written without formatting, in plain text, using a macro language. This means that the document's content can change independently of its formatting and vice versa.
 +
 
 +
:; Features : ConTeXt supports colors, configurable page backgrounds, hyperlinks, presentations, figure-text integration, cross-references, bibliographies, indices, typesetting for [[Chemistry|chemistry]] and [[Command/unit|physics]], [[Modes|conditional compilation]], non-latin languages, and [[Imposition|binding and imposition]].
 +
 
 +
:; Graphics : ConTeXt integrates a superset of [[MetaPost]] called [[MetaFun - MetaPost in ConTeXt|MetaFun]], which allows drawing page backgrounds and ornaments.
 +
 
 +
:; Internationalization : ConTeXt provides a multi-lingual user interface with support for markup in English, Dutch, German, French, and Italian and support for output in many languages including western European languages, eastern European languages, Arabic, Chinese, Japanese, and Korean.
 +
 
 +
:; Compatibility : ConTeXt supports TeX engines such as [[wikipedia:pdfTeX|pdfTeX]], [[XeTeX]], and [[LuaTeX]] without changing the user interface.
 +
 
 +
:; History : ConTeXt was developed from 1990 by Hans Hagen from [http://www.pragma-ade.com/ PRAGMA Advanced Document Engineering] (Pragma ADE), a Netherlands-based company.  See [[ConTeXt history]] for further details.
 +
 
 +
:; Licensing : ConTeXt is [http://en.wikipedia.org/wiki/free_software free software]. The program code (i.e. anything not under the <code>/doc</code> subtree) is distributed under the [http://en.wikipedia.org/wiki/GNU_GPL GNU GPL]; the documentation is provided under [http://en.wikipedia.org/wiki/Creative_Commons Creative Commons] Attribution NonCommercial ShareAlike license.
 +
 
 +
:; Example : A simple ConTeXt document resembles:
 +
 
 +
<context source="yes" text="This produces:">
 +
\setuphead[section][color=red]
 +
 
 +
\starttext
 +
 
 +
\section{Hello}
 +
World!
 +
 
 +
\stoptext
 +
</context>
 +
 
 +
:; Technical Details
 +
::: ConTeXt can be used to typeset complex and large collections of documents, like educational materials, user guides and technical manuals. Such documents often have high demands regarding structure, design and accessibility. Ease of maintenance, reuse of content and typographic consistency are important prerequisites.
 +
::: ConTeXt is developed for those who are responsible for producing such documents. ConTeXt is written in the typographical programming language TeX. For using ConTeXt, no TeX programming skills and no technical background are needed. Some basic knowledge of typography and document design will enable you to use the full power of ConTeXt.
 +
::: ConTeXt is parameter driven and the user interface supports several languages, like English, German and Dutch. This means that those less familiar with the English language can choose the interface that suits them best. Of course ConTeXt can typeset in many languages.
 +
::: Originally ConTeXt was written as tool for writing complex, constantly changing and extensive educational documents. Although much functionality originates there, ConTeXt has proven to be quite suitable to perform many other complex typesetting tasks. Some features are:
 +
:::* automatic placement of figures, formulas, tables and other kind of floating bodies
 +
:::* automatic generation of lists of abbreviations, synonyms, and whatever needs to be sorted
 +
:::* automatic numbering of footnotes
 +
:::* adapting footers and headers to the current page content
 +
:::* extensive formatting of itemizations in many levels
 +
:::* consistent typesetting of legends to formulas
 +
:::* maintaining several registers, if needed with extensive interactive support
 +
:::* extensive cross-referencing capabilities
 +
:::* generating lists of used figures, tables, formulas and more
 +
:::* forcing rigourous consistency in emphasizing parts of the text
 +
:::* managing documents in a project environment
 +
:::* automatic placement of marginal notes
 +
:::* typesetting in more than one column
 +
:::* identifying textual elements in such a way that they can be hidden, moved and reused when needed (questions, answers, definitions, etc.)
 +
:::* using text in more that one document, with a different layout if needed
 +
:::* automatic hyphenation of words as well as adaptation to language specific typographic needs
 +
:::* inclusion of illustrations in standardized formats from other applications
 +
:::* using color
 +
:::* easy change of layout, while guarding consistent typography
 +
:::* providing multiple tables of contents and lists, at all levels, to provide optimal accessibility
 +
:::* automatic numbering of definitions, lemmas and other structural components
 +
:::* automatic numbering of figures, tables, and other floating bodies
 +
:::* automatic makeup of tables and formulas
 +
 
 +
::: ConTeXt supports the PDF format and is able to directly produce highly interactive PDF files, using pdfTeX. All cross-references are automatically converted to hyperlinks. Such documents can be viewed and consulted with Acrobat. ConTeXt can provide all kinds of navigational aids that can be activated without programming. Electronic versions of documents thereby become very useful in educational settings. The potential of PDF is available to the user: complex forms and JavaScripts are no problem for ConTeXt. [http://www.pragma-ade.nl/ PRAGMA ADE] has developed ConTeXt in-house mainly to suit its own and customers' wishes concerning developing educational documents. Flexibility in layout, reuse of content, and maintenance are keywords.
 +
 
 +
=== How does ConTeXt versioning work? ===
 +
 
 +
: In short, there are 3 major version branches:
 +
:* 1995: ConTeXt [[Mark II]], which defaulted to the pdfTeX engine, but also supported ε-TEX, XeTeX, and Aleph. Now in maintenance-only mode.
 +
:* 2005: ConTeXt [[Mark IV]], using the LuaTeX engine. This is the current stable version.
 +
:* 2019: ConTeXt [[LMTX]], using the new LuaMetaTeX engine. This is the current development version.
 +
: Each of the releases in those major branches also has an ISO timestamp that functions as a minor version number.
 +
: See [[ConTeXt history]] for further details.
  
=== Is ConTeXt free (open source) software? ===
+
== Starting with ConTeXt ==
:Yes.  See the [[Read Me]] page for details.
 
  
 
=== How do I install ConTeXt? ===
 
=== How do I install ConTeXt? ===
 +
:See [[Installation]]
 +
 +
=== Is there a hello-world document? ===
 +
:Yes.  See [[First Document]] and [[Detailed Example]].
  
:See [[Installation]]
+
=== Is ConTeXt free (libre, open source) software? ===
 +
:Yes.  See the [[Read Me]] page for details.
  
 
=== Does ConTeXt support Unicode? ===
 
=== Does ConTeXt support Unicode? ===
:Yes. It supports Unicode (utf-8) input, with the <cmd>enableregime</cmd><tt>[utf-8]</tt> command. See also [[Encodings and Regimes]]  (This needs a bit of elaboration!) If you use [[XeTeX]], Unicode should work by default.
+
:Yes. It supports Unicode (UTF-8). In [[XeTeX]] and [[LuaTeX]] it is the default input encoding, while you need to use <cmd>enableregime</cmd><tt>[utf-8]</tt> command when working with [[pdfTeX]]. See also [[Encodings and Regimes - Old Content]]  (This needs a bit of elaboration!)
  
=== Why does <code>\startalignment[right]</code> or <code>\framed[align=right]{some text}</code> align my text left instead of right and vice versa? ===
+
=== Why should I only use letters, digits and hyphens in file/path names? ===
:This is for backward compatibility with older versions; see [[Right and left]]. Hans was originally thinking of "ragged right" and "ragged left" alignment.  Use '''flushleft''' and '''flushright''' instead.
+
:Please see section "Files" of the [http://pmrb.free.fr/contextref.pdf ConTeXt manual]. And also [http://www.ntg.nl/pipermail/ntg-context/2011/057342.html here] for some discussion on the mailing-list.
 +
 
 +
== ConTeXt vs. LaTeX ==
  
 
=== What are the differences between ConTeXt and LaTeX? ===
 
=== What are the differences between ConTeXt and LaTeX? ===
Line 31: Line 105:
  
 
:Author: Brooks Moses on c.t.t. usenet
 
:Author: Brooks Moses on c.t.t. usenet
 +
 +
:(Note that the internal coding of ConTeXt has become much easier, too, with the use of LuaTeX - or perhaps seemingly more complicated, as one has to then learn lua to understand the internal workings of ConTeXt. Most users will never delve into this level, but do indeed benefit from the increased performance of the ConTeXt system. The loading of the ConTeXt macros and the processing of even very large typesetting projects is not slow!)
  
 
=== What are the advantages of ConTeXt over LaTeX? ===
 
=== What are the advantages of ConTeXt over LaTeX? ===
Line 37: Line 113:
  
 
:Source: ''LaTeX in proper ConTeXt'' (by Berend de Boer)
 
:Source: ''LaTeX in proper ConTeXt'' (by Berend de Boer)
 +
 +
=== What are the advantages of LaTeX over ConTeXt? ===
 +
 +
:It has been a long battle to get publishers of scientific journals, for example, to accept submissions coded in LaTeX. Currently, submitting a ConTeXt document to such journals or to open repositories such as arXiv is problematic. This is one reason to continue using LaTeX for such work.
 +
 +
:Another advantage is that many good books on LaTeX exist. Documentation of ConTeXt is not satisfactory, as attested by much activity on the mailing list, but is slowly being improved. And good books on the use of ConTeXt need to be written!
 +
 +
=== How transcribe this LaTeX macro to ConTeXt? ===
 +
Could you please advice me, how transcribe this macro, controlling that no last line of a paragraph is shorter than the paragraph indenting?
 +
 +
<texcode>
 +
\parfillskip=\hsize
 +
\advance\parfillskip by -1.5\parindent
 +
\advance\parfillskip by 0pt minus \parfillskip
 +
\advance\parfillskip by 0pt minus -1em
 +
</texcode>
 +
 +
Like this:
 +
<texcode>
 +
\installalign
 +
  {block}
 +
  {\parfillskip=\hsize
 +
  \advance\parfillskip by -1.5\parindent
 +
  \advance\parfillskip by 0pt minus \parfillskip
 +
  \advance\parfillskip by 0pt minus -1em}
 +
 +
% followed by
 +
\setupalign[block]
 +
</texcode>
 +
 +
== XML and other formats ==
  
 
=== How can I convert a document into RTF or HTML? ===
 
=== How can I convert a document into RTF or HTML? ===
Line 50: Line 157:
 
:[http://archive.contextgarden.net/thread/20050926.213139.45057948.en.html DOC/RTF to ConTeXt via XML]
 
:[http://archive.contextgarden.net/thread/20050926.213139.45057948.en.html DOC/RTF to ConTeXt via XML]
  
 +
=== XML: please tell me more about it ===
 +
There is a section on the wiki dedicated to typesetting [[XML]] under the various flavours of ConTeXt.
  
=== Can I change to Computer Modern's LaTeX font? ===
+
== Fonts and Typography ==
  
I see diferences in screen between default fonts in ConTeXt (latin modern) and LaTeX (computer modern). Can I swicth to latex default font?. I think it's more stetical
+
=== Can I change to LaTeX’s Computer Modern font? ===
 +
 
 +
I see differences in screen between default fonts in ConTeXt (Latin Modern) and LaTeX (Computer Modern). Can I switch to LaTeX default font?. I think it's more aesthetical.
 
: No.
 
: No.
 
: ''(I mean - of course you can; you only need to modify a few type-xxx.tex files and replace lm with cm in the source. But that solution is not/will not be supported officially.)''
 
: ''(I mean - of course you can; you only need to modify a few type-xxx.tex files and replace lm with cm in the source. But that solution is not/will not be supported officially.)''
 
:: Is there any tutorial for doing it?
 
:: Is there any tutorial for doing it?
 
::: ''No. There are no tutorials for the things that one is not supposed to mess with. Take a look at how things are done in those files and replace any occurrence of lm with cm.''
 
::: ''No. There are no tutorials for the things that one is not supposed to mess with. Take a look at how things are done in those files and replace any occurrence of lm with cm.''
 +
: There might be a workaround for this. Install the [http://cm-unicode.sourceforge.net/ OpenType version of Computer Modern fonts] on your system and use it with <code>simplefonts</code>.
 +
 +
=== How can I get the “oldstyle numbers” (text figures) in a document? ===
 +
The mediaeval numbers can be inserted locally via the font switch <code>\os</code>.
 +
 +
With OpenType fonts that come with text figures you can just ''add'' the respective
 +
font feature to the set of font features.
 +
 +
<texcode>
 +
\definefontfeature[default][default][onum=yes]
 +
 +
\setupbodyfont[schola,8pt]
 +
 +
\starttext
 +
1234567890
 +
\stoptext
 +
</texcode>
 +
 +
or
 +
 +
<texcode>
 +
\setupbodyfont[schola,8pt]
 +
 +
\definefontfeature[oldstyle][onum=yes]
 +
 +
\starttext
 +
1234567890 {\addff{oldstyle}1234567890}
 +
\stoptext
 +
</texcode>
 +
 +
See mailing list discussion at http://www.ntg.nl/pipermail/ntg-context/2011/058394.html .
  
=== Can I use some simpler biography method? ===
+
(You can check whether your font supports the “onum” feature by running
 +
<code>otfinfo -f</code> on the OTF file.)
  
I see that the method of [[http://wiki.contextgarden.net/Bibliography adding references in ConTexT]] is like bibtex in latex. Is there any simple methood like build-in latex method (\thebibliography)?
+
== Alignment ==
 +
 
 +
=== Why does <code>\startalignment[right]</code> or <code>\framed[align=right]{some text}</code> align my text left instead of right and vice versa? ===
 +
:This is for backward compatibility with older versions; see [[Right and left]]. Hans was originally thinking of "ragged right" and "ragged left" alignment. Use '''flushleft''' and '''flushright''' instead.
  
=== XML: please tell me more about it ===
+
=== Why is \framed{} not centred? ===
 +
<texcode>
 +
\starttext
 +
\startalignment[middle]
 +
  \framed{middle?}
 +
\stopalignment
 +
\startalignment[middle]
 +
  middle!
 +
\stopalignment
 +
\stoptext
 +
</texcode>
  
=== How do I make a presentation? ===
+
Answer: \framed switches to vmode, so you need \dontleavehmode:
 +
<texcode>
 +
\starttext
 +
\startalignment[middle]
 +
  \dontleavehmode
 +
  \framed{middle!}
 +
\stopalignment
 +
\stoptext
 +
</texcode>
  
:You don't need any special package (like prosper or seminar in LaTeX) to make a presentation. In contrast to LaTeX, changing the document size, changing colors, adding hyperlinks, ... appears to be extremely simple in ConTeXt. See [[Presentations]] for more specific topics.
+
== Spacing ==
  
 
=== <code>\setupindenting[medium]</code> doesn't work? ===
 
=== <code>\setupindenting[medium]</code> doesn't work? ===
 +
:This does work, but the effect is not what you expect. Without <code>yes</code>, you have now set up the default size, but you have not turned paragraph indenting on. You have to execute <code>\setupindenting[yes]</code> before it starts actually indenting your paragraphs.
 +
 +
=== How can I get a horizontal space with a defined width, so as ex. "\hspace{3em}" or "\hspace*{3em}" in LaTeX? ===
 +
:A horizontal space can be inserted with the TeX-Primitive <code>\hskip〈dimension〉</code> or with the ConTeXt command <cmd>hspace</cmd><tt>[identifier]</tt>.
 +
 +
=== Why is there a line-break in the output after some commands? ===
 +
<texcode>
 +
\starttext
 +
\externalfigure[hacker][width=1cm] Why a new line here?
 +
\stoptext
 +
</texcode>
 +
 +
Answer: \externalfigure switches to vmode, so you need \dontleavehmode:
 +
<texcode>
 +
\starttext
 +
\dontleavehmode
 +
\externalfigure[hacker][width=1cm] Same line!
 +
\stoptext
 +
</texcode>
  
:This does work, but the effect is not what you expect. Without <code>yes</code>, you have now set up the default size, but you have not turned paragraph indenting on. You have to execute <code>\setupindenting[yes]</code> before it starts actually indenting your paragraphs.
+
== Math ==
  
 
=== Does $$...$$ work for display math, like in (La)TeX? ===
 
=== Does $$...$$ work for display math, like in (La)TeX? ===
:No; the spacing above and below the equation will be wrong, and maybe other aspects too.  Instead use <cmd>startformula</cmd> and <cmd>stopformula</cmd>.
+
:No; the spacing above and below the equation will be wrong, and maybe other aspects too.  Instead use <cmd>startformula</cmd> and <cmd>stopformula</cmd> (just as one rather generally prefers to use <cmd>begin{equation}</cmd> and <cmd>end{equation}</cmd> in LaTeX).
  
 
=== How do I get a numbered equation? ===
 
=== How do I get a numbered equation? ===
 
:Add <cmd>placeformula</cmd> before the <cmd>startformula</cmd>.
 
:Add <cmd>placeformula</cmd> before the <cmd>startformula</cmd>.
  
=== How can I get a horizontal space with a defined width, so as ex. "\hspace{3em}" or "\hspace*{3em}" in LaTeX? ===
+
== Misc ==
:A horizontal space can be inserted with the TeX-Primitive<cmd>hspace〈dimension〉</cmd> or with the ConTeXt command <cmd>hspace[identifier]</cmd>.
+
 
 +
=== Can I use some simpler bibliography method? ===
 +
 
 +
I see that the method of [[http://wiki.contextgarden.net/Bibliography adding references in ConTexT]] is like bibtex in latex. Is there any simple methood like build-in latex method (\thebibliography)?
 +
: Perhaps [[http://wiki.contextgarden.net/Simple_Bibliography Simple bibliography (in simple bibliography)]]?
  
=== How can I get the lowercase (medieval, oldstyle figures) numbers in a document? ===
+
=== How do I make a presentation? ===
The mediaeval numbers can be inserted locally by "\os". I would prefer a global setting of them but I don't know how to do it.
 
  
=== How transcribe this LaTeX macro to ConTEXt? ===
+
:You don't need any special package (like prosper or seminar in LaTeX) to make a presentation. In contrast to LaTeX, changing the document size, changing colors, adding hyperlinks, ... appears to be extremely simple in ConTeXt. See [[Presentations]] for more specific topics.
Could you please advice me, how transcribe this macro, controlling that no last line of a paragraph is shorter than the paragraph indenting?
 
  
<texcode>
+
[[Category:Basics]]
\parfillskip=\hsize
 
\advance\parfillskip by -1.5\parindent
 
\advance\parfillskip by 0pt minus \parfillskip
 
\advance\parfillskip by 0pt minus -1em
 
</texcode>
 

Revision as of 12:35, 2 July 2020


TODO: This FAQ needs to have a lot of things worked on. To avoid clutter from repeated TODO tags, just note missing answers with "...", and put notes about missing information in parentheses. (See: To-Do List)


ConTeXt General

What is ConTeXt?

ConTeXt is a document production system, based on Donald Knuth's TeX, for typesetting high-quality documents. More specifically, it is both:
  • a set of high-level macros written in the (somewhat arcane) TeX language, and these macros simplify the task of designing layouts, making hyperlinks, etc.
  • and a set of software and tools for moving from these macros to high-quality digital documents.
Unlike familiar word processors where the formatting of the final document is crafted while writing the content, ConTeXt documents are written without formatting, in plain text, using a macro language. This means that the document's content can change independently of its formatting and vice versa.
Features 
ConTeXt supports colors, configurable page backgrounds, hyperlinks, presentations, figure-text integration, cross-references, bibliographies, indices, typesetting for chemistry and physics, conditional compilation, non-latin languages, and binding and imposition.
Graphics 
ConTeXt integrates a superset of MetaPost called MetaFun, which allows drawing page backgrounds and ornaments.
Internationalization 
ConTeXt provides a multi-lingual user interface with support for markup in English, Dutch, German, French, and Italian and support for output in many languages including western European languages, eastern European languages, Arabic, Chinese, Japanese, and Korean.
Compatibility 
ConTeXt supports TeX engines such as pdfTeX, XeTeX, and LuaTeX without changing the user interface.
History 
ConTeXt was developed from 1990 by Hans Hagen from PRAGMA Advanced Document Engineering (Pragma ADE), a Netherlands-based company. See ConTeXt history for further details.
Licensing 
ConTeXt is free software. The program code (i.e. anything not under the /doc subtree) is distributed under the GNU GPL; the documentation is provided under Creative Commons Attribution NonCommercial ShareAlike license.
Example 
A simple ConTeXt document resembles:
\setuphead[section][color=red]

\starttext

\section{Hello}
World!

\stoptext

This produces:

Technical Details
ConTeXt can be used to typeset complex and large collections of documents, like educational materials, user guides and technical manuals. Such documents often have high demands regarding structure, design and accessibility. Ease of maintenance, reuse of content and typographic consistency are important prerequisites.
ConTeXt is developed for those who are responsible for producing such documents. ConTeXt is written in the typographical programming language TeX. For using ConTeXt, no TeX programming skills and no technical background are needed. Some basic knowledge of typography and document design will enable you to use the full power of ConTeXt.
ConTeXt is parameter driven and the user interface supports several languages, like English, German and Dutch. This means that those less familiar with the English language can choose the interface that suits them best. Of course ConTeXt can typeset in many languages.
Originally ConTeXt was written as tool for writing complex, constantly changing and extensive educational documents. Although much functionality originates there, ConTeXt has proven to be quite suitable to perform many other complex typesetting tasks. Some features are:
  • automatic placement of figures, formulas, tables and other kind of floating bodies
  • automatic generation of lists of abbreviations, synonyms, and whatever needs to be sorted
  • automatic numbering of footnotes
  • adapting footers and headers to the current page content
  • extensive formatting of itemizations in many levels
  • consistent typesetting of legends to formulas
  • maintaining several registers, if needed with extensive interactive support
  • extensive cross-referencing capabilities
  • generating lists of used figures, tables, formulas and more
  • forcing rigourous consistency in emphasizing parts of the text
  • managing documents in a project environment
  • automatic placement of marginal notes
  • typesetting in more than one column
  • identifying textual elements in such a way that they can be hidden, moved and reused when needed (questions, answers, definitions, etc.)
  • using text in more that one document, with a different layout if needed
  • automatic hyphenation of words as well as adaptation to language specific typographic needs
  • inclusion of illustrations in standardized formats from other applications
  • using color
  • easy change of layout, while guarding consistent typography
  • providing multiple tables of contents and lists, at all levels, to provide optimal accessibility
  • automatic numbering of definitions, lemmas and other structural components
  • automatic numbering of figures, tables, and other floating bodies
  • automatic makeup of tables and formulas
ConTeXt supports the PDF format and is able to directly produce highly interactive PDF files, using pdfTeX. All cross-references are automatically converted to hyperlinks. Such documents can be viewed and consulted with Acrobat. ConTeXt can provide all kinds of navigational aids that can be activated without programming. Electronic versions of documents thereby become very useful in educational settings. The potential of PDF is available to the user: complex forms and JavaScripts are no problem for ConTeXt. PRAGMA ADE has developed ConTeXt in-house mainly to suit its own and customers' wishes concerning developing educational documents. Flexibility in layout, reuse of content, and maintenance are keywords.

How does ConTeXt versioning work?

In short, there are 3 major version branches:
  • 1995: ConTeXt Mark II, which defaulted to the pdfTeX engine, but also supported ε-TEX, XeTeX, and Aleph. Now in maintenance-only mode.
  • 2005: ConTeXt Mark IV, using the LuaTeX engine. This is the current stable version.
  • 2019: ConTeXt LMTX, using the new LuaMetaTeX engine. This is the current development version.
Each of the releases in those major branches also has an ISO timestamp that functions as a minor version number.
See ConTeXt history for further details.

Starting with ConTeXt

How do I install ConTeXt?

See Installation

Is there a hello-world document?

Yes. See First Document and Detailed Example.

Is ConTeXt free (libre, open source) software?

Yes. See the Read Me page for details.

Does ConTeXt support Unicode?

Yes. It supports Unicode (UTF-8). In XeTeX and LuaTeX it is the default input encoding, while you need to use \enableregime[utf-8] command when working with pdfTeX. See also Encodings and Regimes - Old Content (This needs a bit of elaboration!)

Why should I only use letters, digits and hyphens in file/path names?

Please see section "Files" of the ConTeXt manual. And also here for some discussion on the mailing-list.

ConTeXt vs. LaTeX

What are the differences between ConTeXt and LaTeX?

The main difference between the two, in my opinion, is a philosophical one: LaTeX was created with the idea of separating content and presentation to such an extent that the typical author would write their content and then use a style file created by someone else to provide the visual presentation. Thus, the proliferation of style files and related things.
ConTeXt, on the other hand, retained the idea of separating content and presentation, but was created with the idea of being used for books, where each book tends to have a different layout, and so the expected "end user" is the person doing all the layout. Thus, it's designed to provide a vast amount of flexibility for layout in a way that can be fairly easily defined without needing to write a package (or go find one that's already written).
To some extent, modern LaTeX has become a lot more like ConTeXt's intent, with a large quantity of packages, and classes like "memoir" that are designed to give the end user a large amount of control of the visual presentation. Thus, the difference is more one of focus and arrangement -- ConTeXt is all "of a piece" and most things are built in and designed as a complete set, whereas with LaTeX it's generally the case that when you want to do something different, you need to find the right package, and sometimes find that there are three that almost do what you want and none that are quite right (but, then, that also means that there are usually choices for how to do things, which can be good.)
Another difference is that IMO, ConTeXt is a lot easier to program in. It was designed a fair bit later than LaTeX, for much faster computers, and thus includes a lot of things that make it load and run slower but make programming a lot easier.
Author: Brooks Moses on c.t.t. usenet
(Note that the internal coding of ConTeXt has become much easier, too, with the use of LuaTeX - or perhaps seemingly more complicated, as one has to then learn lua to understand the internal workings of ConTeXt. Most users will never delve into this level, but do indeed benefit from the increased performance of the ConTeXt system. The loading of the ConTeXt macros and the processing of even very large typesetting projects is not slow!)

What are the advantages of ConTeXt over LaTeX?

ConTeXt is a macro package that’s far more advanced than LaTeX. You can enhance LaTeX with third party packages, but not all macro packages work together with each other. ConTeXt is an integrated, powerful and flexible macro package for which you seldom need third party packages. ConTeXt also has been used to create large and complex on-screen documents, including hyperlinks, on screen buttons, forms, cross-document links, and so on.
Source: LaTeX in proper ConTeXt (by Berend de Boer)

What are the advantages of LaTeX over ConTeXt?

It has been a long battle to get publishers of scientific journals, for example, to accept submissions coded in LaTeX. Currently, submitting a ConTeXt document to such journals or to open repositories such as arXiv is problematic. This is one reason to continue using LaTeX for such work.
Another advantage is that many good books on LaTeX exist. Documentation of ConTeXt is not satisfactory, as attested by much activity on the mailing list, but is slowly being improved. And good books on the use of ConTeXt need to be written!

How transcribe this LaTeX macro to ConTeXt?

Could you please advice me, how transcribe this macro, controlling that no last line of a paragraph is shorter than the paragraph indenting?

\parfillskip=\hsize
\advance\parfillskip by -1.5\parindent
\advance\parfillskip by 0pt minus \parfillskip
\advance\parfillskip by 0pt minus -1em

Like this:

\installalign
  {block}
  {\parfillskip=\hsize
   \advance\parfillskip by -1.5\parindent
   \advance\parfillskip by 0pt minus \parfillskip
   \advance\parfillskip by 0pt minus -1em}

% followed by
\setupalign[block]

XML and other formats

How can I convert a document into RTF or HTML?

Hot topic on the mailing list!
There's currently no converter such as LaTeX2html available for ConTeXt. If you're ready to pay a price and put some more effort in your document, the best way is to use XML and produce PDF out of it with ConTeXt and HTML using XSLT.
ConTeXt to RTF Conversion

What about the other way around?

DOC/RTF to ConTeXt via XML

XML: please tell me more about it

There is a section on the wiki dedicated to typesetting XML under the various flavours of ConTeXt.

Fonts and Typography

Can I change to LaTeX’s Computer Modern font?

I see differences in screen between default fonts in ConTeXt (Latin Modern) and LaTeX (Computer Modern). Can I switch to LaTeX default font?. I think it's more aesthetical.

No.
(I mean - of course you can; you only need to modify a few type-xxx.tex files and replace lm with cm in the source. But that solution is not/will not be supported officially.)
Is there any tutorial for doing it?
No. There are no tutorials for the things that one is not supposed to mess with. Take a look at how things are done in those files and replace any occurrence of lm with cm.
There might be a workaround for this. Install the OpenType version of Computer Modern fonts on your system and use it with simplefonts.

How can I get the “oldstyle numbers” (text figures) in a document?

The mediaeval numbers can be inserted locally via the font switch \os.

With OpenType fonts that come with text figures you can just add the respective font feature to the set of font features.

\definefontfeature[default][default][onum=yes]

\setupbodyfont[schola,8pt]

\starttext
1234567890
\stoptext

or

\setupbodyfont[schola,8pt]

\definefontfeature[oldstyle][onum=yes]

\starttext
1234567890 {\addff{oldstyle}1234567890}
\stoptext

See mailing list discussion at http://www.ntg.nl/pipermail/ntg-context/2011/058394.html .

(You can check whether your font supports the “onum” feature by running otfinfo -f on the OTF file.)

Alignment

Why does \startalignment[right] or \framed[align=right]{some text} align my text left instead of right and vice versa?

This is for backward compatibility with older versions; see Right and left. Hans was originally thinking of "ragged right" and "ragged left" alignment. Use flushleft and flushright instead.

Why is \framed{} not centred?

\starttext
\startalignment[middle]
  \framed{middle?}
\stopalignment
\startalignment[middle]
  middle!
\stopalignment
\stoptext

Answer: \framed switches to vmode, so you need \dontleavehmode:

\starttext
\startalignment[middle]
  \dontleavehmode
  \framed{middle!}
\stopalignment
\stoptext

Spacing

\setupindenting[medium] doesn't work?

This does work, but the effect is not what you expect. Without yes, you have now set up the default size, but you have not turned paragraph indenting on. You have to execute \setupindenting[yes] before it starts actually indenting your paragraphs.

How can I get a horizontal space with a defined width, so as ex. "\hspace{3em}" or "\hspace*{3em}" in LaTeX?

A horizontal space can be inserted with the TeX-Primitive \hskip〈dimension〉 or with the ConTeXt command \hspace[identifier].

Why is there a line-break in the output after some commands?

\starttext
\externalfigure[hacker][width=1cm] Why a new line here?
\stoptext

Answer: \externalfigure switches to vmode, so you need \dontleavehmode:

\starttext
\dontleavehmode
\externalfigure[hacker][width=1cm] Same line!
\stoptext

Math

Does $$...$$ work for display math, like in (La)TeX?

No; the spacing above and below the equation will be wrong, and maybe other aspects too. Instead use \startformula and \stopformula (just as one rather generally prefers to use \begin{equation} and \end{equation} in LaTeX).

How do I get a numbered equation?

Add \placeformula before the \startformula.

Misc

Can I use some simpler bibliography method?

I see that the method of [adding references in ConTexT] is like bibtex in latex. Is there any simple methood like build-in latex method (\thebibliography)?

Perhaps [Simple bibliography (in simple bibliography)]?

How do I make a presentation?

You don't need any special package (like prosper or seminar in LaTeX) to make a presentation. In contrast to LaTeX, changing the document size, changing colors, adding hyperlinks, ... appears to be extremely simple in ConTeXt. See Presentations for more specific topics.