J.4. Building the Documentation with Meson
  Two options are provided for building the documentation using Meson.
    Change to the
  
   build
  
  directory before running
    one of these commands, or add
  
   -C build
  
  to the command.
 
To build just the HTML version of the documentation:
build$ninja docs
To build all forms of the documentation:
build$ninja alldocs
  The output appears in the
    subdirectory
  
   build/doc/src/sgml
  
  .