htacces Path Rewrite to get Contents From a Different Folder - .htaccess

Question

How do you do a simple path rewrite in .htaccess? I need my localhost/blog url to access the content located in localhost/assets/blog . How do I make this rule occur in htaccess?
My full .htaccess code:
<IfModule mod_rewrite.c>
Options +FollowSymlinks -MultiViews
RewriteEngine On
</IfModule>
RewriteCond %{HTTP_HOST} ^www.mysite.com$ [NC]
RewriteRule ^(.*)$ http://mysite.com/$1 [R=301,L,S=4]
# If requested resource exists as a file or directory, skip next three rules
RewriteCond %{DOCUMENT_ROOT}/$1 -f [OR]
RewriteCond %{DOCUMENT_ROOT}/$1 -d
RewriteRule (.*) - [S=3]
# Blog articles.
# RewriteCond %{REQUEST_FILENAME} !-f
# RewriteCond %{REQUEST_FILENAME} !-d
# RewriteRule ^/?blog/([^/]+)/(\d+)/(\d+)$ blog.php?title=$1&id=$2&reply_to=$3 [L,S=1]
# RewriteCond %{REQUEST_FILENAME} !-f
# RewriteCond %{REQUEST_FILENAME} !-d
# RewriteRule ^/?blog/([^/]+)/(\d+)$ blog.php?title=$1&id=$2 [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(blog/.*)$ /assets/$1 [L,NC]
# Remove the .php extension
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^([^\.]+)$ $1.php [NC,L]
# for copying
#RewriteCond %{REQUEST_FILENAME} !-f
#RewriteCond %{REQUEST_FILENAME} !-d
#RewriteRule ^(.*)$ index.php?page=$1 [L]
RewriteRule (.*)\.xml(.*) $1.php$2 [nocase]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ app.php?tag=$1 [QSA,L]
# ----------------------------------------------------------------------
# Custom 404 page
# ----------------------------------------------------------------------
# You can add custom pages to handle 500 or 403 pretty easily, if you like.
ErrorDocument 403 /error.php?type=403
ErrorDocument 404 /error.php?type=404
ErrorDocument 500 /error.php?type=500

Answer 1

Enable mod_rewrite and .htaccess through httpd.conf and then put this code in your .htaccess under DOCUMENT_ROOT directory:
Options +FollowSymLinks -MultiViews
# Turn mod_rewrite on
RewriteEngine On
RewriteBase /
RewriteRule ^(blog/.*)$ /assets/$1 [L,NC]
RewriteRule ^assets/ - [L,NC]