Hi Mikael and Otared,

I can confirm issues regarding primes, too. If you are using the STIX 2 fonts (http://www.stixfonts.org <http://www.stixfonts.org/>) and my example below you get a somewhat strange behaviour of primes that is pretty obvious. I think the issues should be fixed.

By the way the issue seems to depend to some extend on the fonts. Using Lucida by \setupbodyfont[lucidaot] it is not that obvious but still present. Using Latin Modern it seems that the spacing between the primes changes between f'' and f^{''}. Cambria seems to show that behaviour (like Latin Modern), too, but less obvious.

Best regards
Mathias

%% example 
\unprotect

\definefontfeature
	[stixtwo-math-feature]
	[kern=yes,
		ss01=no,    % calligraphic letters
		ss02=yes,	% lowercase italic variants (e.g. open g)
		ss03=no,	% hbar und lambdabar variants
		ss04=yes,	% larger and lower primes, minute etc.
		ss05=no,	% shorter arrows
		ss06=no,	% narrower and shorter element and similar symbols
		ss07=no,	% some smaller operators and emptyset variant
		ss08=yes,	% upright integrals etc.
		ss09=no,	% variant negated symbols
		ss10=yes,	% variants of greater and lesser and similar symbols
		ss11=yes,	% variant of negated set (inclusion etc.) symbols
		ss14=yes,	% 
		ss16=yes]	% variants of circled operators

\starttypescriptcollection[Stix2]
	
	\starttypescript [\s!serif] [Stix2] [\s!all]
		\definefontsynonym
            [Stix2Regular]
            [file:STIX2Text-Regular.otf]
        \definefontsynonym
            [Stix2Bold]
            [file:STIX2Text-Bold.otf]
        \definefontsynonym
            [Stix2Italic]
            [file:STIX2Text-Italic.otf]
        \definefontsynonym
            [Stix2BoldItalic]
            [file:STIX2Text-BoldItalic.otf]      
        \definefontsynonym[\s!Serif] [Stix2Regular] [\s!features=\s!default]
        \definefontsynonym[\s!SerifBold] [Stix2Bold] [\s!features=\s!default]
        \definefontsynonym[\s!SerifItalic] [Stix2Italic] [\s!features=\s!default]
        \definefontsynonym[\s!SerifBoldItalic] [Stix2BoldItalic] [\s!features=\s!default]
    \stoptypescript
    
    \starttypescript [\s!math] [Stix2]
        \definefontsynonym
            [Stix2Math]
            [file:STIX2Math.otf]
            [features=math\mathsizesuffix]
        \definefontsynonym [\s!MathRoman] [Stix2Math] [\s!features={\s!math\mathsizesuffix,mathextra,stixtwo-math-feature},\s!designsize=\s!auto]
    \stoptypescript

    \starttypescript [Stix2]
        \definetypeface [\typescriptone] [\s!rm] [\s!serif] [Stix2] [\s!default]
        \definetypeface [\typescriptone] [\s!mm] [\s!math] [Stix2] [\s!default]
    \stoptypescript

\stoptypescriptcollection

\protect

\setupbodyfont[Stix2]

\starttext
%
Compare $f'$ to $(f')$ and to $f''$, $(f'')$, $f^{''}$ and $(f^{''})$.
%
\stoptext
%% end of example



> Am 22.05.2017 um 09:50 schrieb Otared Kavian <otared@gmail.com>:
> 
> Hi Mikael,
> 
> You are correct, the position of \prime depends on whether there is a next character or not after it, and it seems that this has an effect on its position for characters having a subscript as in
> 	$f_{1}''(x) \neq f''_{1}(x)$ 
> 	$f'f''f'’'$
> Best regards: OK
> 
>> On 22 May 2017, at 08:51, Mikael P. Sundqvist <mickep@gmail.com> wrote:
>> 
>> On Sun, May 21, 2017 at 10:29 PM, Otared Kavian <otared@gmail.com> wrote:
>>> Hi Mikael,
>>> 
>>> I agree with what you are reporting: the current behavior of the \prime operator is not completely satisfying when using ConTeXt mkiv, while in mkii it is the most satisfying (in my opinion…).
>>> 
>>> The turn around consisting in using $f^{‘’}$ or  $f^{\prime\prime}$, or even $f^{{}^{\prime\prime}}$, is not really satisfying either.
>>> 
>>> But I think (or I hope that) at some point Hans will fix it in mkiv.
>>> 
>>> Best regards: OK
>>> 
>>>> On 21 May 2017, at 08:14, Mikael P. Sundqvist <mickep@gmail.com> wrote:
>>>> […]
>>>> 
>>>> And just for reference, the document below gives the attached pdf,
>>>> compiled with lualatex. I think the location of the primes there look
>>>> better. Sorry for spamming about this issue, but I think it is
>>>> important for all people writing math with ConTeXt.
>>>> 
>>>> /Mikael
>>>> 
>>>> \RequirePackage{luatex85}
>>>> \documentclass[border=2pt]{standalone}
>>>> 
>>>> \usepackage{unicode-math}
>>>> \setmainfont{LucidaBrightOT}
>>>> \setmathfont{LucidaBrightMathOT}
>>>> 
>>>> \begin{document}
>>>> $f'f''$
>>>> \end{document}
>>>> <lltest.pdf>___________________________________________________________________________________
>>>> If your question is of interest to others as well, please add an entry to the Wiki!
>>>> 
>>>> maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
>>>> webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
>>>> archive  : https://bitbucket.org/phg/context-mirror/commits/
>>>> wiki     : http://contextgarden.net
>>>> ___________________________________________________________________________________
>>> 
>>> ___________________________________________________________________________________
>>> If your question is of interest to others as well, please add an entry to the Wiki!
>>> 
>>> maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
>>> webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
>>> archive  : https://bitbucket.org/phg/context-mirror/commits/
>>> wiki     : http://contextgarden.net
>>> ___________________________________________________________________________________
>> 
>> Otared, thank you for confirmation. I also hope there will be a fix soon.
>> 
>> In the meantime, I put yet another test file. The location of the
>> primes depends on the next character (I use, at the moment current
>> version: 2017.05.15 21:48)
>> 
>> /Mikael
>> 
>> \definefontfamily[myface][rm][Lucida Bright OT]
>> \definefontfamily[myface][mm][Lucida Bright Math OT]
>> \setupbodyfont[myface,10pt]
>> \starttext
>> \startTEXpage[offset=2pt]
>> $f'(x)f''(x)f'f''$
>> \stopTEXpage
>> \stoptext
>> <primfisk.pdf>___________________________________________________________________________________
>> If your question is of interest to others as well, please add an entry to the Wiki!
>> 
>> maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
>> webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
>> archive  : https://bitbucket.org/phg/context-mirror/commits/
>> wiki     : http://contextgarden.net
>> ___________________________________________________________________________________
> 
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to the Wiki!
> 
> maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
> archive  : https://bitbucket.org/phg/context-mirror/commits/
> wiki     : http://contextgarden.net
> ___________________________________________________________________________________