CellProlog
is an option to Cell that gives an expression to evaluate before each ordinary evaluation of the contents of the cell.
Details

- CellProlog:>expr evaluates expr for every ordinary kernel evaluation done in the cell, as initiated for example by
or by Evaluate in Place.
- CellProlog is not evaluated for evaluations associated with Dynamic objects.
- The default setting is CellProlog->None.
- CellProlog is often set at a style or notebook level, rather than for individual cells.
Examples
Applications (2)
Wolfram Research (2007), CellProlog, Wolfram Language function, https://reference.wolfram.com/language/ref/CellProlog.html.
Text
Wolfram Research (2007), CellProlog, Wolfram Language function, https://reference.wolfram.com/language/ref/CellProlog.html.
CMS
Wolfram Language. 2007. "CellProlog." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/CellProlog.html.
APA
Wolfram Language. (2007). CellProlog. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/CellProlog.html