View source for Category:Pages using Math with unknown parameters

{{Unknown parameters category|1=Math}}

''Note'': the following code habit is not an error.

:<code><nowiki>{{math|{1, 2, 3}</nowiki>{{bg|yellow|{{!}}<nowiki>}}</nowiki>}}</code> is not an error, and should be left unedited.

:In code: <code><nowiki>the indices can range over the set {{math|{1, 2, 3}|}}</nowiki></code>
:Text shown: "... the indices can range over the set {{math|{1, 2, 3}|}}"
The extra pipe symbol in <code><nowiki>{{math|{1, 2, 3}</nowiki>{{bg|yellow|{{!}}<nowiki>}}</nowiki>}}</code> is unused but does not corrupt the math text. It ''helps'' understanding the input text (distinguishing the various }-symbol). 

It produces a categorisation here, and a Warning: "{{red|1=unknown parameter {{!}}2=}}". However, since it is helpful, it is not an error, and it should not be edited out. {{As of|Jan 2021}}, 18 articles are listed with this feature.