Bug in DeclarePairedDelimitersXPP

[xiaoniu-578fa6bff964d005]

Issue Summary

If DeclarePairedDelimitersXPP in MathJax should have same function as DeclarePairedDelimiterXPP in LaTeX, then it should substitute pre and post part.

Steps to Reproduce:

The following doesn't work normally.

$\DeclarePairedDelimitersXPP\norm[2]{}{\lVert}{\rVert}{_{#1}}{#2}$
$\norm{2}{2}$

Technical details:

• MathJax Version: 3.2.0
• Client OS: Mac OS X 12.01
• Browser: Safari 15.1

Supporting information:

I believe this is related to this implementation.
Body, pre, post should all be substituted with arguments.

[dpvc]

Thanks for the report. You are correct about the location of the issue, and that pre and post should also include substitution just as body does.