The `\SetTracking` command does not override the inter-word spacing setup of a previous `\SetTracking` unless the tracking values are also different

[linguisticturn]

Description

The \SetTracking command does not override the inter-word spacing setup of a previous \SetTracking command unless the tracking values are different as well in the two commands. Tested with pdflatex and all TeXLive versions from 2014 to 2024 (i.e. all versions of TeXLive available on OverLeaf).

First reported on the TeX StackExchange here: https://tex.stackexchange.com/questions/736655/microtypes-settracking-command-does-not-override-the-inter-word-spacing-setup .

The issue is not limited to the spacing optional argument, but also appears for e.g. outer spacing , outer kerning, and probably all other optional arguments (though I haven't tested all of them).

Minimal example demonstrating the issue

\documentclass[12pt]{report}
\usepackage{microtype}
\microtypesetup{tracking=true,spacing=true,activate=true} % I don't think this is necessary, but I'm including it just in case
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{calc}
\usepackage[left=0.25in,top=0.25in]{geometry}
\usepackage{parskip}
%
\begin{document}

{
\SetTracking[spacing={600*,,}]{encoding = * }{ 160 }
Stop \textls{stealing sheep}!\\
}
{ 
\SetTracking[spacing={6000*,,}]{encoding = * }{ 160 } % if this is used, the inter-word spacing remains 600*
% \SetTracking[spacing={6000*,,}]{encoding = * }{ 161 } % if this is used, the inter-word spacing does become 6000*
Stop \textls{stealing sheep}!
}
\end{document}

in the .log file, one finds the following (here the name of the compiled file is spacing.tex):

Package microtype Warning: tracking amount list 'spacing.tex/17' will

(microtype)                            override list 'spacing.tex/13' for

(microtype)                            font 'T1////' on input line 17.

So it seems like the second \SetTracking command should override the first. But that only happens if the tracking value in the second \SetTracking command is even a little bit different from that in the first, i.e. if it's 160 in the first and 161 in the second.

[cfr42]

Note that this is reproducible with LuaTeX and XeTeX - it is not specific to pdfTeX.

\documentclass{article}
\usepackage{fontspec}
\usepackage{microtype}
\begin{document}
{%
  \SetTracking[spacing={600*,,}]{encoding = * }{ 160 }
  Stop \textls{stealing sheep}!

}
Stop stealing sheep!

\textls{Stop stealing sheep}!

{%
  \SetTracking[spacing={6000*,,}]{encoding = * }{ 160 }
  Stop \textls{stealing sheep}!

}
\end{document}

It is not entirely clear to me from the documentation whether these settings are intended to be modified in this way or not. But, even if this is unintended usage, perhaps microtype could provide some kind of warning for this case (and not just warn because the default settings are being overridden).

prawf-2.luatex.log
prawf-2.xetex.log

[schlcht]

The problem is that microtype only checks the desired letterspacing amount (ie. the second mandatory argument to \SetTracking) to see whether it should reinitialise a font. So if both fonts are to be letterspaced by the same amount, microtype would assume that that's the same font with no other changes required. In theory, it would of course be possible to also check all relevant options (from the optional argument), too, but that would necessitate a lot more bookkeeping and might slow down things quite a bit. I'll have a look at it, but cannot promise that it won't be considered as a "known limitation". (Not anytime soon, though, sorry, I'm overwhelmed with other things at the moment...)

(As an aside to @cfr42's point, the settings are actually not supposed to be modified this way (that's why you get a warning), but rather by means of the context option, so something like this in the preamble:

\SetTracking[context=one, spacing={600*,,}]{encoding = * }{ 160 } % or no context
\SetTracking[context=two, spacing={6000*,,}]{encoding = * }{ 160 }

and then in the document itself:

\microtypecontext{tracking=one} % etc.

but that wouldn't change anything with respect to the problem at hand.)

[cfr42]

Also (for an example using the context as explained by @schlcht above): https://tex.stackexchange.com/q/752633/.

[peaR-red]

I suppose one can segregate the cache hash by injecting the list name \MT@tr@c@name into the \MT@lsfont definition in order to force TeX to associate distinct tracking options with distinct font instances.

For example, instead of

    \xdef\MT@lsfont{\csname\expandafter\string\font@name
            /\number\MT@letterspace@ ls\endcsname}%

we can do

    \xdef\MT@lsfont{\csname\expandafter\string\font@name
            /\number\MT@letterspace@
            /\MT@tr@c@name ls\endcsname}%

Then, we shift the outer kerning and spacing caches to target this new, completely unique \MT@lsfont. For example, we will now do:

    \MT@outer@space=\csname MT@outer@space\expandafter\string\MT@lsfont\endcsname\relax
    \xdef\MT@set@curr@os{\MT@outer@space=\the\MT@outer@space\relax}%
    \MT@tr@outer@l
    \ifx\MT@ls@adjust\@empty
      \MT@outer@kern=-\dimexpr\MT@letterspace@ sp * \fontdimen6\font@name/2000\relax
      \MT@ls@outer@k
    \else
      \MT@outer@kern=\expandafter\expandafter\expandafter\@firstoftwo
                     \csname MT@outer@kern\expandafter\string\MT@lsfont\endcsname\relax
      \ifdim\MT@outer@kern=\z@\else \MT@ls@outer@k \fi
      \MT@outer@kern=\expandafter\expandafter\expandafter\@secondoftwo
                      \csname MT@outer@kern\expandafter\string\MT@lsfont\endcsname\relax

and

\def\MT@tr@set@space#1,#2,#3,#4,#5,#6,{%
  \let\MT@temp\@empty
  \MT@tr@set@space@{#1}{#4}{2}\@empty
  \MT@tr@set@space@{#2}{#5}{3}\@plus
  \MT@tr@set@space@{#3}{#6}{4}\@minus
  \MT@glet@nc{MT@outer@space\expandafter\string\MT@lsfont}\MT@temp
  % ...debug code
}

\def\MT@tr@set@okern#1,#2,{%
  \let\MT@temp\@empty
  \MT@ifempty{#1}{\MT@tr@set@okern@{*}}{\MT@tr@set@okern@{#1}}%
  \MT@ifempty{#2}{\MT@tr@set@okern@{*}}{\MT@tr@set@okern@{#2}}%
  \MT@glet@nc{MT@outer@kern\expandafter\string\MT@lsfont}\MT@temp
  % ...debug code
}

---

Demonstration of the patch (compiled with pdflatex):

\documentclass[12pt]{report}
\usepackage{microtype}
\microtypesetup{tracking=true,spacing=true,activate=true}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{calc}
\usepackage[left=0.25in,top=0.25in]{geometry}
\usepackage{parskip}
\makeatletter
\def\MT@set@tr@codes{%
  \MT@vinfo{Tracking font `\MT@@font'\on@line}%
  \MT@requires@pdftex8\@firstofone{%
    \MT@ifdefined@n@TF{\MT@@font-fake6}{%
      \MT@exp@cs\ifx{\MT@@font-fake6}\@empty
        \MT@warning@nl{%
          Font `\MT@@font' does not specify its\MessageBreak
          \@backslashchar fontdimen 6 (width of an `em')! Therefore,\MessageBreak
          tracking will not work with this font}%
        \MT@glet@nc{\MT@@font-fake6}\relax
      \fi
    }%
  }{%
  \MT@if@list@exists
    \MT@get@tr@opt
    \relax
  \MT@ifdefined@c@TF\MT@letterspace@\relax{\let\MT@letterspace@\MT@letterspace}%
  \ifnum\MT@letterspace@=\z@
    \MT@set@tr@zero
  \else
    \MT@vinfo{... Tracking by \number\MT@letterspace@}%
    \MT@warn@tracking@DVI
    \xdef\MT@lsfont{\csname\expandafter\string\font@name
                           /\number\MT@letterspace@/\MT@tr@c@name ls\endcsname}%
    \expandafter\ifx\MT@lsfont\relax
      \MT@get@ls@basefont
      \global\expandafter\letterspacefont\MT@lsfont\font@name\MT@letterspace@
      \MT@ifdefined@c@TF\MT@tr@ispace
        {\let\@tempa\MT@tr@ispace}%
        {\edef\@tempa{\MT@letterspace@*,,}}%
      \MT@ifdefined@c@TF\MT@tr@ospace
        {\edef\@tempa{\@tempa,\MT@tr@ospace}}%
        {\edef\@tempa{\@tempa,,,}}%
      \expandafter\MT@tr@set@space\@tempa,%
      \MT@ifdefined@c@TF\MT@tr@okern{\let\@tempa\MT@tr@okern}{\def\@tempa{*,*}}%
      \expandafter\MT@tr@set@okern\@tempa,%
      \MT@ifdefined@c@T\MT@tr@ligatures\MT@tr@noligatures
      \MT@do@font{\lpcode\MT@lsfont\@tempcnta=\numexpr\MT@letterspace@/2\relax
                  \rpcode\MT@lsfont\@tempcnta=\numexpr\MT@letterspace@/2\relax}%
      \let\MT@the@pr@code\MT@the@pr@code@tr
    \fi
    \aftergroup\MT@set@lsfont
    \let\MT@font\MT@lsfont
    \xdef\MT@set@curr@ls{\def\noexpand\MT@curr@ls{\MT@letterspace@}}%
    \aftergroup\MT@set@curr@ls
    \MT@outer@space=\csname MT@outer@space\expandafter\string\MT@lsfont\endcsname\relax
    \xdef\MT@set@curr@os{\MT@outer@space=\the\MT@outer@space\relax}%
    \MT@tr@outer@l
    \ifx\MT@ls@adjust\@empty
      \MT@outer@kern=-\dimexpr\MT@letterspace@ sp * \fontdimen6\font@name/2000\relax
      \MT@ls@outer@k
    \else
      \MT@outer@kern=\expandafter\expandafter\expandafter\@firstoftwo
                      \csname MT@outer@kern\expandafter\string\MT@lsfont\endcsname\relax
      \ifdim\MT@outer@kern=\z@\else \MT@ls@outer@k \fi
      \MT@outer@kern=\expandafter\expandafter\expandafter\@secondoftwo
                      \csname MT@outer@kern\expandafter\string\MT@lsfont\endcsname\relax
    \fi
    \xdef\MT@set@curr@ok{\MT@outer@kern=\the\MT@outer@kern\relax}%
    \MT@afteraftergroup{%
      \MT@set@curr@os
      \MT@set@curr@ok
      \noexpand\MT@tr@outer@r
    }%
  \fi
  }%
}

\def\MT@tr@set@space#1,#2,#3,#4,#5,#6,{%
  \let\MT@temp\@empty
  \MT@tr@set@space@{#1}{#4}{2}\@empty
  \MT@tr@set@space@{#2}{#5}{3}\@plus
  \MT@tr@set@space@{#3}{#6}{4}\@minus
  \MT@glet@nc{MT@outer@space\expandafter\string\MT@lsfont}\MT@temp
}

\def\MT@tr@set@okern#1,#2,{%
  \let\MT@temp\@empty
  \MT@ifempty{#1}{\MT@tr@set@okern@{*}}{\MT@tr@set@okern@{#1}}%
  \MT@ifempty{#2}{\MT@tr@set@okern@{*}}{\MT@tr@set@okern@{#2}}%
  \MT@glet@nc{MT@outer@kern\expandafter\string\MT@lsfont}\MT@temp
}
\makeatother
\begin{document}

{
\SetTracking[spacing={600*,,}]{encoding = * }{ 160 }
Stop \textls{stealing sheep}!\\
}
{ 
\SetTracking[spacing={6000*,,}]{encoding = * }{ 160 }
Stop \textls{stealing sheep}!
}
\end{document}

Another one with the example from TeX.SE, referenced by @cfr42

% Source - https://tex.stackexchange.com/q/752633
% Posted by FKranhold, modified by community. See post 'Timeline' for change history
% Retrieved 2026-04-17, License - CC BY-SA 4.0

\documentclass{article}
\usepackage[tracking=smallcaps]{microtype}

\SetTracking[context=a,outerspacing={ 300,,}]{encoding=*,shape=sc}{200}
\SetTracking[context=b,outerspacing={1000,,}]{encoding=*,shape=sc}{ 10}
\makeatletter
\def\MT@set@tr@codes{%
  \MT@vinfo{Tracking font `\MT@@font'\on@line}%
  \MT@requires@pdftex8\@firstofone{%
    \MT@ifdefined@n@TF{\MT@@font-fake6}{%
      \MT@exp@cs\ifx{\MT@@font-fake6}\@empty
        \MT@warning@nl{%
          Font `\MT@@font' does not specify its\MessageBreak
          \@backslashchar fontdimen 6 (width of an `em')! Therefore,\MessageBreak
          tracking will not work with this font}%
        \MT@glet@nc{\MT@@font-fake6}\relax
      \fi
    }%
  }{%
  \MT@if@list@exists
    \MT@get@tr@opt
    \relax
  \MT@ifdefined@c@TF\MT@letterspace@\relax{\let\MT@letterspace@\MT@letterspace}%
  \ifnum\MT@letterspace@=\z@
    \MT@set@tr@zero
  \else
    \MT@vinfo{... Tracking by \number\MT@letterspace@}%
    \MT@warn@tracking@DVI
    \xdef\MT@lsfont{\csname\expandafter\string\font@name
                           /\number\MT@letterspace@/\MT@tr@c@name ls\endcsname}%
    \expandafter\ifx\MT@lsfont\relax
      \MT@get@ls@basefont
      \global\expandafter\letterspacefont\MT@lsfont\font@name\MT@letterspace@
      \MT@ifdefined@c@TF\MT@tr@ispace
        {\let\@tempa\MT@tr@ispace}%
        {\edef\@tempa{\MT@letterspace@*,,}}%
      \MT@ifdefined@c@TF\MT@tr@ospace
        {\edef\@tempa{\@tempa,\MT@tr@ospace}}%
        {\edef\@tempa{\@tempa,,,}}%
      \expandafter\MT@tr@set@space\@tempa,%
      \MT@ifdefined@c@TF\MT@tr@okern{\let\@tempa\MT@tr@okern}{\def\@tempa{*,*}}%
      \expandafter\MT@tr@set@okern\@tempa,%
      \MT@ifdefined@c@T\MT@tr@ligatures\MT@tr@noligatures
      \MT@do@font{\lpcode\MT@lsfont\@tempcnta=\numexpr\MT@letterspace@/2\relax
                  \rpcode\MT@lsfont\@tempcnta=\numexpr\MT@letterspace@/2\relax}%
      \let\MT@the@pr@code\MT@the@pr@code@tr
    \fi
    \aftergroup\MT@set@lsfont
    \let\MT@font\MT@lsfont
    \xdef\MT@set@curr@ls{\def\noexpand\MT@curr@ls{\MT@letterspace@}}%
    \aftergroup\MT@set@curr@ls
    \MT@outer@space=\csname MT@outer@space\expandafter\string\MT@lsfont\endcsname\relax
    \xdef\MT@set@curr@os{\MT@outer@space=\the\MT@outer@space\relax}%
    \MT@tr@outer@l
    \ifx\MT@ls@adjust\@empty
      \MT@outer@kern=-\dimexpr\MT@letterspace@ sp * \fontdimen6\font@name/2000\relax
      \MT@ls@outer@k
    \else
      \MT@outer@kern=\expandafter\expandafter\expandafter\@firstoftwo
                      \csname MT@outer@kern\expandafter\string\MT@lsfont\endcsname\relax
      \ifdim\MT@outer@kern=\z@\else \MT@ls@outer@k \fi
      \MT@outer@kern=\expandafter\expandafter\expandafter\@secondoftwo
                      \csname MT@outer@kern\expandafter\string\MT@lsfont\endcsname\relax
    \fi
    \xdef\MT@set@curr@ok{\MT@outer@kern=\the\MT@outer@kern\relax}%
    \MT@afteraftergroup{%
      \MT@set@curr@os
      \MT@set@curr@ok
      \noexpand\MT@tr@outer@r
    }%
  \fi
  }%
}

\def\MT@tr@set@space#1,#2,#3,#4,#5,#6,{%
  \let\MT@temp\@empty
  \MT@tr@set@space@{#1}{#4}{2}\@empty
  \MT@tr@set@space@{#2}{#5}{3}\@plus
  \MT@tr@set@space@{#3}{#6}{4}\@minus
  \MT@glet@nc{MT@outer@space\expandafter\string\MT@lsfont}\MT@temp
}

\def\MT@tr@set@okern#1,#2,{%
  \let\MT@temp\@empty
  \MT@ifempty{#1}{\MT@tr@set@okern@{*}}{\MT@tr@set@okern@{#1}}%
  \MT@ifempty{#2}{\MT@tr@set@okern@{*}}{\MT@tr@set@okern@{#2}}%
  \MT@glet@nc{MT@outer@kern\expandafter\string\MT@lsfont}\MT@temp
}
\makeatother
\begin{document}
\the\pdfelapsedtime

Some \textmicrotypecontext{tracking=a}{\scshape word} inbetween.

Some \textmicrotypecontext{tracking=b}{\scshape word} inbetween.

Some \textmicrotypecontext{tracking=a}{\scshape word} inbetween.

Some \textmicrotypecontext{tracking=b}{\scshape word} inbetween.

\end{document}

[peaR-red]

In theory, it would of course be possible to also check all relevant options (from the optional argument), too, but that would necessitate a lot more bookkeeping and might slow down things quite a bit.

Probably not too much? The patch doesn't seem to affect compilation time by a noticeable amount (at least with pdflatex), so perhaps it might be worth implementing.