code: private Object getValue(PageContext pc, SQL sql, Query querySource, int row, Collection.Key key, Object value) throws PageException {
  	if (value instanceof ZSelectItem) return executeExp(pc, sql, querySource, ((ZSelectItem) value).getExpression(), row);
  	return querySource.getAt(key, row);
      }
docs: return value
  
  @param sql
  @param querySource
  @param row
  @param key
  @param value
  @return value
  @throws PageException