https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#cother-other-default-operation-rules "The compiler is more likely to get the default semantics right and you cannot implement these functions better than the compiler."
This also improves Commonmark coverage, e.g. it fixes tests HTML_blocks_ex179_2894..2906 and Lists_ex308_5439..5457. In other words, we go from 271 out of 652 to 273 out of 652.