The website seems to be generated by doxygen, and the config is in the tools/doxygen/Doxyfile, there is a bunch of options to tweak, I tried to change the INPUT, EXTRACT_PRIVATE, INTERNAL_DOCS, and it adds more classes to the website, I added this two lines, and there is the doc for skparagraph, icluding private impl classes
the default INPUT is like so
https://skia.googlesource.com/skia/+/refs/heads/main/tools/doxygen/Doxyfile#793 and it includes
some of the public api