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PublishedAPI for packages intended to be used by Plugin and Contrib authors, or 
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See also 
Developing plugins, 
Developer's Bible, 
Technical Overview
Node visitor interface for traversing a .spec tree
--++ 
ObjectMethod startVisit($node) → $boolean
Called on each node in the tree as a visit starts.
Return 1 to continue the visit, or 0 to terminate it.
--++ 
ObjectMethod endVisit($node) → $boolean
Called on each node in the tree as a visit finishes.
Return 1 to continue the visit, or 0 to terminate it.