The most common kind of controller; effectively a controller linked to a {@link DataObject}.

ContentControllers are most useful in the content-focused areas of a site. This is generally
the bulk of a site; however, they may be less appropriate in, for example, the user management
section of an application.
On its own, content controller does very little. Its constructor is passed a which is stored in $this->dataRecord. Any unrecognised method calls, for example, Title()
and Content(), will be passed along to the data record,
Subclasses of ContentController are generally instantiated by ModelAsController; this will create
a controller based on the URLSegment action variable, by looking in the SiteTree table.