/*!

  \defgroup jkqtmathtext_fonthandling Font Handling
  \ingroup jkqtmathtext_general
  


    As LaTeX also does, fonts are set by font classes. These are defined in JKQTMathTextEnvironmentFont:
      - A "roman" (MTEroman / MTEmathRoman) font used as the standard font ( JKQTMathText::setFontRoman() and for use in math mode JKQTMathText::setFontMathRoman() )
      - A "sans-serif" (MTEsans / MTEmathSans) font which may be activated with \c \\sf ... ( JKQTMathText::setFontSans() and for use in math mode JKQTMathText::setFontMathSans()  )
      - A "typewriter" (MTEtypewriter) font which may be activated with \c \\tt ... ( JKQTMathText::setFontTypewriter() )
      - A "script" (MTEscript) font which may be activated with \c \\script ... ( JKQTMathText::setFontScript() )
      - A "math-roman" (MTEmathRoman) font used as the standard font in math mode ( JKQTMathText::setFontMathRoman() )
      - A "math-sans-serif" (MTEmathSans) used as sans serif font in math mode ( JKQTMathText::setFontMathSans() )
      - A "blackboard" (MTEblackboard) font used to display double stroked characters ( JKQTMathText::setFontBlackboard() )
      - A "caligraphic" (MTEcaligraphic) font used to display caligraphic characters ( JKQTMathText::setFontCaligraphic() )
      - A "fraktur" (MTEfraktur) font used to display fraktur characters ( JKQTMathText::setFontFraktur() )
      - A fallback font MTEFallbackSymbols for (math) symbols, greek letters ... (if the symbols are not present in the currently used font). ( JKQTMathText::setFallbackFontSymbols() )
    .

    The default font class is "roman" (i.e. MTEroman in text-mode and MTEmathRoman in math-mode). You can switch to
    "sans-serif" by using LaTeX commands like \c \\sf .

    Especially when using the library in the context of a GUI, usually a sans-serif font is used to typeset text in the GUI
    as these are generally better readable on a screen than serif fonts. Therefore when using JKQTMathText for GUI rendering,
    it makes sense to redefine the class "roman" with the GUI font. You can e.g. write:
    \code
        JKQTMathText::setFontRoman(QGuiApplication::font().family(), MTFEUnicode);
        JKQTMathText::setFontMathRoman(QGuiApplication::font().family(), MTFEUnicode);
        JKQTMathText::setFontSize(QGuiApplication::font().pointSize());
    \endcode
    or the short hand:
    \code
        JKQTMathText::setFontRomanAndMath(QGuiApplication::font().family(), MTFEUnicode);
    \endcode
    With JKQTMathTextFontSpecifier::fromFontSpec() there is a third way that allows to use a special string syntax (handy for INI files)
    to define fonts, see JKQTMathTextFontSpecifier . You can e.g. simply write:
    \code
        JKQTMathText::setFontRomanAndMath("application+XITS", MTFEUnicode);
    \endcode
    In all cases the default GUI font is used for rendering default output. For \c \\sf to make a difference you can additionally
    set the "sans" class as a serif font, e.g.:
    \code
        JKQTMathText::setFontSans("serif");
        JKQTMathText::setFontMathSans("serif");
    \endcode
    Using the font name \c "serif" will cause Qt to lookup a suitable serif font.


    These fonts are generic font classes, which font is actually used can be configured in JKQTMathText
    class with the \c set...() functions mentioned above. Additionally some short ahnds exist:
      - JKQTMathText::useSTIX() use the STIX fonts from <a href="https://www.stixfonts.org/">https://www.stixfonts.org/</a> in math-mode (or math- and text-mode, additionally also as MTEFallbackSymbols)<br>\image html jkqtmathtext/jkqtmathtext_stix.png
      - JKQTMathText::useXITS() use the XITS fonts from <a href="https://github.com/alif-type/xits">https://github.com/alif-type/xits</a> in math-mode (or math- and text-mode, additionally also as MTEFallbackSymbols). These are included by default in this library and also activated by default.<br>\image html jkqtmathtext/jkqtmathtext_xits.png
      - JKQTMathText::useASANA() use the ASANA fonts from <a href="https://ctan.org/tex-archive/fonts/Asana-Math/">https://ctan.org/tex-archive/fonts/Asana-Math/</a> in math-mode (or math- and text-mode, additionally also as MTEFallbackSymbols)<br>\image html jkqtmathtext/jkqtmathtext_asana.png
      - JKQTMathText::useAnyUnicode() set fonts for "roman" and "sans" in text- and math-mode with one call
      - JKQTMathText::useAnyUnicodeForMathOnly() set fonts for "roman" and "sans" in math-mode only with one call, leaves text-mode fonts as is
      - JKQTMathText::useAnyUnicodeForTextOnly() set fonts for "roman" and "sans" in text-mode only with one call, leaves math-mode fonts as is
      - JKQTMathText::setFontRomanAndMath() set "roman" font in text- and math-mode
      - JKQTMathText::setFontRomanOrSpecial() use an object of type JKQTMathTextFontSpecifier or a special string syntax (see struct documentation
        of JKQTMathTextFontSpecifier) to define the text- and math-mode "roman" fonts
    .

    Here are some examples of using different, widely available, fonts:
        - using "Arial" <c>JKQTMathText::setFontRomanAndMath("Arial")</c>: \image html jkqtmathtext/jkqtmathtext_arial.png
        - using "Courier New" <c>JKQTMathText::setFontRomanAndMath("Courier New")</c>: \image html jkqtmathtext/jkqtmathtext_couriernew.png
        - using "Comic Sans MS" <c>JKQTMathText::setFontRomanAndMath("Comic Sans MS")</c>: \image html jkqtmathtext/jkqtmathtext_comicsans.png
        - using "Old English Text" <c>JKQTMathText::setFontRomanAndMath("Old English Text")</c>: \image html jkqtmathtext/jkqtmathtext_OldEnglish.png
        - using "Computer Modern" <c>JKQTMathText::setFontRomanAndMath("CMU Serif")</c>: \image html jkqtmathtext/jkqtmathtext_computermodern.png
        - using <a href="https://en.wikipedia.org/wiki/Fira_(typeface)">"Fira"</a> <c>JKQTMathText::setFontRoman("Fira Sans"); setFontMathRoman("Fira Math")</c>: \image html jkqtmathtext/jkqtmathtext_fira.png
        - using "MS Segoe UI" (the default Win 10/11 GUI font) <c>JKQTMathText::setFontRomanAndMath("MS Segoe UI")</c>: \image html jkqtmathtext/jkqtmathtext_mssegoeui.png
        - using <a href="https://dejavu-fonts.github.io/">"DejaVu Sans"</a> <c>JKQTMathText::setFontRomanAndMath("DejaVu Sans")</c>: \image html jkqtmathtext/jkqtmathtext_DejaVuSans.png
        - using <a href="https://dejavu-fonts.github.io/">"DejaVu Serif"</a> <c>JKQTMathText::setFontRomanAndMath("DejaVu Serif")</c>: \image html jkqtmathtext/jkqtmathtext_DejaVuSerif.png
        - using "XITS" <c>JKQTMathText::useXITS(false)</c>: \image html jkqtmathtext/jkqtmathtext_xits_all.png
    .

    Math-mode is activated by enclosing your equation in \c $...$ or \c \\[...\\] .
    This mode is optimized for mathematical equations. Here is an example of the difference:
      - <b>math-mode</b>:
          - use fonts MTEmathRoman and MTEmathSans
          - whitespaces are mostly not drawn directly
          - symbol spacing is different
          - an example: \image html jkqtmathtext/schreq_mathmode.png
        .
      - <b>text-mode</b>:
          - use fonts MTEroman and MTEsans
          - whitespaces are evaluated directly
          - an example: \image html jkqtmathtext/schreq_normalmode.png
    .

    Font Lookup for symbols works as follows in JKQTMathTextSymbolNode:
      - if a character is found in the current (or to be used) font, it is taken from there
      - if the character is not found, it is looked for in the fallback fonts MTEFallbackSymbols
      - as a last resort, some symbols can be created otherwise, so if neither of the two options above
        contain the required symbol, the symbol might be synthesized otherwise, or a rectangle with the size of "X" is drawn instead
    .

    In "normal text", i.e. JKQTMathTextTextNode no font-lookup is perfomed, i.e. if a acharacter
    is not available in the selected font, it is not typeset (or typeset with a replacement, like a box).
    There are exceptions to this rule however: For some special fonts a lookup or synthetisation of
    the characters is performed. Currently this is implemented for:
      - "blackboard", the options are defined by setBlackboardFontMode(). See JKQTMathTextBlackboradDrawingMode
    .
    
*/