Kigezo:!(
[
This is the {{!(}} meta-template.
This is an auxiliary template allowing to use (encode) "[" in template or parser function parameters. It is necessary if the character is used in some parser functions. If you're only looking for the graphical representation of an opening square bracket without the syntactical meaning, use [.
For example:
{{#ifeq: {{str left|[[Foo]]|2}} | [[ | Yes | No }}→{{#ifeq: [[ | [[ | Yes | No }}, fails since rightmost pairs of brackets/braces have precedence in the MediaWiki parser{{#ifeq: {{str left|[[Foo]]|2}} | [[ | Yes | No }}→Yes, fails since "[" and "[" simply have different internal representations.{{#ifeq: {{str left|[[Foo]]|2}} | {{!(}}{{!(}} | Yes | No }}→Yes, works.