There are several typos and grammar problems on this documentation page:
Unity Manual > Graphics > Graphics Overview > Cameras Overview > Occlusion Culling (Pro only)

With my local Unity installation the URL to this page is:
file:///Applications/Unity/Unity.app/Contents/Documentation/html/en/Manual/OcclusionCulling.html

Start sentences with capital letters here:
"…the view frustrum only. this technique…"
"…using portal culling. this technique…"

Fix typo:
"… set to the largest far clip planed…"
Change it to this:
"… set to the largest far clip plane…"

Remove extraneous "is" from this phrase:
"…create Occlusion Areas is by adding…"

End this sentence with a period:
"… to an empty game object (Component->Rendering->Occlusion Area in the menus)"

Change to plural "primitives" here:
"…to create occlusion primitive which are…"

Some of the items above are duplicated on the following pages and should be changed there as well:

Unity Manual > Graphics > Graphics Reference > Rendering Components > Occlusion Area (Pro Only)
file:///Applications/Unity/Unity.app/Contents/Documentation/html/en/Manual/class-OcclusionArea.html

Unity Manual > Graphics > Graphics Reference > Rendering Components > Occlusion Portals
file:///Applications/Unity/Unity.app/Contents/Documentation/html/en/Manual/class-OcclusionPortal.html