It is completely automatic, and has no user-definable parameters.
Sample output
Because this template is dependent upon detecting a PAGENAME that is a century, its output can only be seen on a century page. It is impossible to reproduce its results here. If you wish to test it, go to any century and add {{timeline}} to the page.
Special note
Please remember that the word "century" should not be capitalized in the PAGENAME of any new century page that you create.
ultimately will use {{#sub:{{PAGENAME}}|0|2}} as the core engine prolly have to throw in some #if or #switch thingies to capture centuries that are 1 or 3 numbers in length. {{{1|{{#expr:{{#sub:{{PAGENAME}}|0|2}} -1}} }}} -1 or +1 gives prev and next cent and should assign to the variable {{{1}}} for decades {{#sub:{{PAGENAME}}|0|4}}