This means one can write pages using whatever means desired such as a WYSIWYG web editor, or autogenerating pages from a backend process.
Installation is difficult as it requires modifying the .htaccess file.
The wgHTML home page has a long and useful discussion thread concerning the development of this module.
The README has misleading documentation on the configuration of .htaccess. What I just added is the following:
RewriteCond %{REQUEST_URI} \.html?$|\.txt$|\.doc$|\.me$ [NC]
RewriteRule ^(.*)$ index.php?q=/wghtml/show [L]
This goes in the standard .htaccess file just before the <IfModule>. Note the RewriteCond does not include .php as a pattern, so that it does not interfere with PHP execution. One should also drop .doc and .me from this list.
In summary this offers a useful way to edit some pages using a WYSIWYG editor or other means. However it clearly presents an installation challenge.