This is documentation for Mathematica 6, which was
based on an earlier version of the Wolfram Language.
View current documentation (Version 11.1)

CellEvaluationDuplicate

CellEvaluationDuplicate
is an option for Cell which specifies whether the front end should make a copy of the cell before performing any evaluation of its contents that you request.
Create an input cell with CellEvaluationDuplicate set to True:
In[1]:=
Click for copyable input
In[2]:=
Click for copyable input
Select Join[{a, b}, {c, d}] and use EvaluationEvaluate in Place to create a new cell:
In[3]:=
Click for copyable input
New in 3