Uses double quotes instead of single quotes for XPath tests. Take http://www.loc.gov/MARC21/slim namespace into acccount. Sources not referring to this namespace will not work.

Commented stylesheet to make clear that it is only a sample stylesheet.

Added CUSTOMIZEME labels.

Added possibility to drop only subfield of collection identifier instead of
all 980 field.

Changed default dropped field from 980a to 980w.

Some simplification of the stylesheet.