TS:
id for fixed - unique elements
class for repeating elements 

classes in ids used like hooks. Display hidden used to controll layout.
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classical approach comp. http://web.nwe.ufl.edu/writing/help/web/authoring/html/css/div.html
#header
#side
#spacer
#content
#footer

is saying about the location of elements rather then the data which is represented.
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css-contracts (i - initial) (n - new)
toplevel:
#branding (i)
Container used for a header and banner to brand the site. That is the former "top".

#search (i)
Related to search interface and search results

#nav or #navigation (i)
Used to contain the navigation devices

#content (i)
Used for content rather than for another purpose such as navigation

#siteinfo (i)
Used for various site related information

The problem that I am facing if I want to use e.g. the nav container for all nav elements is to still have the same style. 
The style depends on overall (IMO style specific) style-divs that are just for web-design reason. 
That would denegate a single skeleton for css-contracts like css-garden. 
One could introduce a raster approach but that would be more or less the top-main-footer approach.

Breaking down the problem again to #id basis. The pathing of them makes the final style.