Why isn't this mod_rewrite re-directing? - mod-rewrite

Question

I'm sending every request through an index.php except for pages in my blog subdirectory. I've been able to do this using mod_rewrite in my parent folder and;
RewriteCond %{REQUEST_URI} !^/blog
RewriteRule ^(.+)$ index.php?url=$1 [QSA,L]
]
However, I'd also like to send requests to my blog folder if they have the form:
documentation/some-file.
I've tried:
RewriteRule ^/documentation/(.+)$ https://www.some_domain.com/blog/documentation/$1
but it looks like my request isn't getting sent to the blog folder in this case. My full code is below:
RewriteEngine On
#redirect to index.php as appropriate
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-l
RewriteRule ^/documentation/(.+)$ https://www.some_domain.com/blog/documentation/$1
RewriteCond %{REQUEST_URI} !^/blog
RewriteRule ^(.+)$ index.php?url=$1 [QSA,L]
Edit:
I've used a slightly modified version of #Rijul's suggestion below and after moving the RewriteRule to before the RewriteCond, it works as I had hoped. In other words, the re-write for documentation performs the re-write to the blog subfolder. And, all other requests go through my index.php file. At this point, I would like to understand why.
RewriteEngine On
RewriteRule ^documentation/?(.*)$ /blog/documentation/$1 [R=301,L]
#redirect to index.php as appropriate
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-l
RewriteRule ^(.+)$ index.php?url=$1 [QSA,L]

Answer 1

From what i know
RewriteEngine On
Without this all the rewrite rules and condition will be ignore
RewriteRule ^documentation/?(.*)$ /blog/documentation/$1 [R=301,L]
Rewrites documentation to blog/documentation
RewriteCond %{REQUEST_FILENAME} !-d
This rewrite condition checks whether the requested directory name doesn't exits. If it doesn't exits. Then proceeds to the next condition
RewriteCond %{REQUEST_FILENAME} !-f
This rewrite condition checks whether the requested file name doesn't exits. If it doesn't exits. Then proceeds to the next condition
RewriteCond %{REQUEST_FILENAME} !-l
This rewrite condition checks whether the requested symbolic link doesn't exits. If it doesn't exits. Then proceeds to rewrite rule
RewriteRule ^(.+)$ index.php?url=$1 [QSA,L]
Rewrite to index.php?url=
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-l
writing rewrite condition like this produces an and operation.
(no file exits in that name) and (no directory exits in that name) and
(no symbolic link exits in that name)
If this is true then rewrite to php file. (no directory exits in that name) will go false in the case for /blog (since such a directory exits)