I want to create a unique reference in each article. This is done by using catgories with the following template, which extends the PageID with a thematic prefix.
{{Category:{{{1}}}{{PAGEID}}}}
I have integrated it into the article like this
{{{ReferenceID|Item}}}
The text of the template is displayed correctly, but Mediawiki does not recognize it as a category and it is not displayed on the special page "desired categories".
What is the mistake? May there is an other option
The syntax of assigning categories to pages is [[Category:{{{1}}}{{PAGEID}}]], not {{Category:{{{1}}}{{PAGEID}}}}.
The wikicode {{{ReferenceID|Item}}} is meaningful only in a template that has a ReferenceID parametre. The template above, which adds category, hasn't.
If ReferenceID is the name of the template above, it is inserted like this: {{ReferenceID|Item}}, not {{{ReferenceID|Item}}}.
The very idea of creating a category for each page is strange. If you want each page to be accessible by a unique ID, create a redirect like #redirect [[(full page name)]] under the title (theme prefix)/(page id). You may want to store those redirects in a separate namespace.