mjhjmtu

This question is related to this earlier TeX-SE question of mine

I would like to have a proper text subscript using the text command. It does not seem to work with the tikzmath macros. Please see the following MWW:

documentclassstandalone
usepackageamsmath
usepackagetikz
usetikzlibrarymath

%%%To fix the text subscript
%usepackageetoolbox
%makeatletter
%robustifytext
%makeatother 

begindocument
 begintikzpicture

 node at (0,0) $textb_textb$: Correct;

 tikzmathlet test=textb_textb;
 node at (0,-1cm) $test$: Not Correct;

 endtikzpicture
enddocument

As can be seen from the output, the subscript size is not correct:

If I apply the suggest fix, the subscript size is corrected:

My question is the use of etoolbox and robustify the suggested way of fixing the text subscripts, which may have some side effects that I may face in the future, or is there a more robust way of correcting the size?

Note: Use of textrm does not work in the above example, which I used for the problem I have reported in my earlier post.

Add a noexpand can fix it directly. But I would think the robustify approach makes more sense if this is an ongoing issue.

documentclassstandalone
usepackageamsmath
usepackagetikz
usetikzlibrarymath

%%%To fix the text subscript
%usepackageetoolbox
%makeatletter
%robustifytext
%makeatother 

begindocument
 begintikzpicture

 node at (0,0) $textb_textb$: Correct;

 tikzmathlet test=textb_textb;
 node at (0,-1cm) $test$: Not Correct;

 tikzmathlet test=textb_noexpandtextb;
 node at (0,-2cm) $test$: Corrected with noexpand;

 endtikzpicture
enddocument

You can see what's going on if you add showtext after the tikzmath declaration:

> test=macro:
->protect unhbox voidb@x hbox b_protect unhbox voidb@x hbox b.

Indeed, the definition of text is found in amstext.sty:

% amstext.sty, line 28:
DeclareRobustCommandtext%
 ifmmodeexpandaftertext@elseexpandaftermboxfi

You also have to know that tikzmath does full expansion; since text is not found in math mode, it just does mbox. Since at the time of let the meaning of protect is relax, it goes on untouched; then the conditional is expanded and since TeX is not in math mode, you get mboxb, which becomes

leavemodehboxb

and finally unhboxvoidb@xhboxb. This should explain the output of show above.

Possibly you want to evaluate something instead of having b in the argument to text; in this case you need to be careful about what to fully expand and what not.

tikzmathlet test=noexpandtextb_noexpandtextb;

will do, but if instead of b you have something like textbfabc, this will die horribly anyhow.

You need noexpand in front of both occurrences of text, in order to suppress its expansion and get the right version when test is indeed used in math mode.