TYPO3 Core

Besides the common use case to be able to categorize records, it should also be possible to render the categories of a record in frontend.
The basic API in TYPO3 for this use case is the CONTENT object in TypoScript. ("This object is designed to generate content by making it possible to finely select records and rendering them.")

But naming the category table sys_category this is not possible, because a prefix sys_ is not allowed for CONTENT.

e.g. the following would not work to render the categories of pages

page.20 = CONTENT
page.20 {
    table = sys_category
    select {
        pidInList = XYZ
        join = sys_category_record_mm ON sys_category.uid = sys_category_record_mm.uid_local
        where = tablenames = 'pages'
        andWhere = sys_category_record_mm.uid_foreign = {TSFE:page|uid}
        andWhere.insertData = 1
    }
    renderObj = COA
    renderObj {
        10 = TEXT
        10.field = title
        10.wrap = |,
    }
}

Having a userFunc in core for this is IMO not the right way.

Using a query to pages with a join is also only a annoying workaround.