Version of m:Template:xpd (talk, backlinks, edit) with four parameters:
Examples:
"{{concat|pqr|stu|vwx}}" gives "pqrstuvwx" [1]
"{{concat|pqr|stu|vwx}}"
"{{#ifeq:2|3|pqr|stu}}" gives "stu" [2]
"{{#ifeq:2|3|pqr|stu}}"
