Understanding Rewrite Rules for File Protection

http://memberpress.helpscoutdocs.com/article/179-understanding-rewrite-rules

Apache :

# BEGIN MemberPress Rules
<IfModule mod_rewrite.c>

RewriteCond %{HTTP_COOKIE} mplk=([a-zA-Z0-9]+)
RewriteCond /var/www/somesite.com/wp-content/uploads/mepr/rules/%1 -f
RewriteRule ^(.*)$ - [L]

RewriteCond %{REQUEST_URI} !^/(wp-admin|wp-includes|wp-content/plugins|wp-content/themes)
RewriteCond %{REQUEST_URI} \.(zip|gz|tar|rar|doc|docx|xls|xlsx|xlsm|pdf|mp4|m4v|mp3|ts|key|m3u8|ZIP|GZ|TAR|RAR|DOC|DOCX|XLS|XLSX|XLSM|PDF|MP4|M4V|MP3|TS|KEY|M3U8)$
RewriteRule . /wp-content/plugins/memberpress/lock.php [L]

</IfModule>
# END MemberPress Rules