查看“Template:When on basepage”的源代码

{{#switch:
  <!--If no or empty "page" parameter then detect
      basepage/subpage/subsubpage-->
  {{#if:{{{page|}}}
  | {{#if:{{#titleparts:{{{page}}}|0|3}}
    | subsubpage    <!--Subsubpage or lower-->
    | {{#if:{{#titleparts:{{{page}}}|0|2}}
      | subpage
      | basepage
      }}
    }}
  | {{#if:{{#titleparts:{{FULLPAGENAME}}|0|3}}
    | subsubpage    <!--Subsubpage or lower-->
    | {{#if:{{#titleparts:{{FULLPAGENAME}}|0|2}}
      | subpage
      | basepage
      }}
    }}
  }}

| basepage   = {{{1|}}}
| subpage    = {{{2|}}}
| subsubpage = {{{3| {{{2|}}} }}}   <!--Respecting empty parameter on purpose-->
}}<!--End switch--><noinclude>
{{Documentation}}
</noinclude>