During transformation, several POI objects are exposed in the beans map.
Because some of these examples call methods with a return type of "void", the Expressions themselves that do so evaluate to null and the cells that contain them will be blanked out. Note: JEXL Expressions allow String literals to be enclosed in single quotes.
After transformation, the above group of cells looks like this.
The Header and Footer objects are populated, and they are seen when switching to Excel's "Page Layout" View.
Note that any expressions found in a sheet's name, header, or footer are transformed before the sheet itself is transformed. That means that such expressions as above will overwrite whatever content was there previously, whether it was static content or evaluated expressions.