The mset template wraps its argument or arguments in curly brackets. If two arguments are supplied, a pipe mark is placed between them. These are used to delimit a set.
The template is designed for use inside the {{math}} template. It clarifies the template's output and avoids a need to use the magic word {{!}}
or the character-substituting templates {{(}} and {{)}}.
Such notation is not only used with sets, but also Schläfli symbols and perhaps others.
Use this template to wrap an expression. For example,
{{math |1={{mset|0 .. 9}} = {{mset|''n'' | 0 ≤ ''n'' ≤ 9}}}}
produces: