The 'Uniclass Work Sections' clauses 'Suggest' related clauses to specify. However, there may be occasions when you want to link to a clause that is not one of the suggested options, but you already have elsewhere in the specification.
A cornerstone of good specification practice is to say it once, and link to it from all parts of the specification.
The separate support article 'All content' for adding clauses from the content set and in this spec provides details on using this feature to link existing content via the 'In this specification' tab.