Add config option to change MathJax renderer

NEWS.md

@@ -1,5 +1,9 @@
 # CHANGES IN bookdown VERSION 0.41
 
+- New `mathjax-config` option for `bs4_book` and `gitbook` to control MathJax config string (thanks, @bwu62, #1472). The option can be set either in the YAML metadata or as a variable in `pandoc_args`. Currently tested and supported settings:
+  - If empty, defaults to original `TeX-MML-AM_CHTML` which renders all equations in common HTML.
+  - If set to `TeX-AMS-MML_HTMLorMML` renders equations in HTML + CSS (which may look nicer for some equations).
+  - If set to `TeX-MML-AM_SVG` renders equations in SVG.
 
 # CHANGES IN bookdown VERSION 0.40
 

inst/templates/bs4_book.html

@@ -158,7 +158,7 @@ <h2>On this page</h2>
     var script = document.createElement("script");
     script.type = "text/javascript";
     var src = "$if(mathjax)$$mathjax$$endif$";
-    if (src === "" || src === "true") src = "https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.9/latest.js?config=TeX-MML-AM_CHTML";
+    if (src === "" || src === "true") src = "https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.9/latest.js?config=$if(mathjax-config)$$mathjax-config$$else$TeX-MML-AM_CHTML$endif$";
     if (location.protocol !== "file:")
       if (/^https?:/.test(src))
         src = src.replace(/^https?:/, '');

inst/templates/gitbook.html

@@ -205,7 +205,7 @@ <h1>
     var script = document.createElement("script");
     script.type = "text/javascript";
     var src = "$if(mathjax)$$mathjax$$endif$";
-    if (src === "" || src === "true") src = "https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.9/latest.js?config=TeX-MML-AM_CHTML";
+    if (src === "" || src === "true") src = "https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.9/latest.js?config=$if(mathjax-config)$$mathjax-config$$else$TeX-MML-AM_CHTML$endif$";
     if (location.protocol !== "file:")
       if (/^https?:/.test(src))
         src = src.replace(/^https?:/, '');