Thread:Project:Support desk/how to invoke named parameter without explicit value

In designing a template to replace another (so we need to fulfill users' expectations and keep existing parameter usage) in the English Wikipedia running MediaWiki version 1.22wmf12 (bbaecbc) with PhP version 5.3.10-1ubuntu3.6+wmf1 (apache2handler) and MySQL version 5.5.30-MariaDB-mariadb1~precise-log, how do we add a named parameter so that entering no value and no equals sign has the same effect as setting the value to "yes"? (I have a template draft and its results are displayed at my sandbox.) Although another template has the desired feature, trying to copy its source code and make what I wanted from it proved too complicated and time-consuming, because I don't understand all of the internal logic behind that one, so I programmed from scratch.