Feature summary (what you would like to be able to do and where):
Allow changing username in API example

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

We want to try another user name.

Benefits (why should this be implemented?):

Else we must manually fiddle with the URL.

1. Visit https://en.wiktionary.org/wiki/Special:ApiSandbox#action=feedcontributions&user=Example
2. Look for a textbox to change user Example to user Nerd000.