The section "Writing a Visitor" of the Developer's Guide contains this quote:
For instance, if you wanted to count the number of elements in the tree, you need only override the visit(ColumnReference) method.
This is old terminology and shoud be replaced with "column reference"
shawkins: it's mixing terminology. in the engine (from the old metamatrix days) column references are called element symbols, so a lot of the logic refers to them as elements
shawkins: it should use the term column reference instead