Canals opened in the YYY0s category header is used to create categories of the form "Canals opened in the YYY0", where YYY0s is a 4-digit decade.
e.g.
It is not for use on other types of categories, e.g.
The template creates navigation tables and puts the page into the correct parent categories
Usage
edit{{Canals opened in the YYY0s category header}}
No parameters needed.